Chapter XXII: Part 22

To these facts may be added the evidence of Prof. Bang that in the first half of the nineteenth century tuberculosis was brought to Denmark by cattle from Switzerland, Schleswig, and England, and that the same thing is now going on in Sweden and Norway, particularly through English cattle. Also the evidence of M. Sivori, chief of section at the ministry of agriculture, Argentina, who has investigated tuberculosis in that country and who says that "30 or 40 years ago tuberculosis was unknown in Argentine cattle, and it is still unknown among the native (criollo) cattle. Its appearance dates from the introduction of pure breeding animals. Statistics prove that tuberculosis is observed among the grades--above all among those of the Durham and less among the Hereford."

Moreover, the reports of the royal commission of Victoria, Australia, and of the New Zealand department of agriculture show a large proportion of tuberculous cattle in those colonies, where the disease was almost certainly carried by British cattle.

In the same manner that tuberculosis has been carried from Great Britain to Denmark, Sweden, Norway, Argentina, and Australia, it has also been taken to Canada. In one herd of imported cattle slaughtered in the Canadian quarantine station, 13 of the 14 animals were found tuberculous. One of the largest Shorthorn herds in Canada was some time ago tested because an animal from it was condemned when offered for shipment to the United States. This herd was found to be very badly affected, and an effort is being made to eradicate the disease by the Bang method. A Canadian official publication says of another Shorthorn herd, which at one time had a very high reputation, that when an investigation in regard to tuberculosis was recently made the disease was found among ordinary cattle wherever animals from this herd had been introduced, and that this herd, which had been looked upon as one of the greatest benefits to the farming community, was really a danger, because it disseminated tuberculosis among the farmers' herds. Still another well-known herd recently attracted attention because four animals from it offered for export to the United States were all tuberculous.

From December 23, 1900, to February 19, 1901, the period that the department inspector tested all Canadian cattle intended for shipment to the United States, 140 purebred Shorthorns and 3 Shorthorn grades were tested, and of the total number 26, or 18 per cent, reacted. During the first month that this inspection was enforced, and when it may be assumed that the condition of the cattle most nearly represented what it had previously been, 74 cattle were offered for importation, and 18, or 24.3 per cent, were found tuberculous.

In justice to Shorthorn cattle it should be said in this connection that they are probably no more susceptible to tuberculosis than are other breeds, but the disease has been allowed to spread in certain herds and families to such an extent as to give a wrong impression concerning the breed as a whole.

The slaughterhouse statistics of Prussia show 14.6 per cent of the cattle and 2.14 per cent of the hogs to be tuberculous. In Saxony the percentage is 29.13 with cattle and 3.10 with hogs. In the city of Leipzig the figures are 36.4 for cattle and 2.17 for hogs. (Siedamgrotzky.) Of 20,850 animals in Belgium tested with tuberculin in 1896, 48.88 per cent reacted. (Stubbe.) Of 25,439 tested in Denmark from 1893 to 1895, 49.3 per cent reacted; and of 67,263 tested from 1896 to 1898, 32.8 per cent reacted. (Bang.)

Figures available in the United States allow us to make a reliable estimate of the extent of tuberculosis of cattle. The following summary is presented:

_Statistics of tests for tuberculosis in the United States, 1917 to March 1, 1922._

-----------------------+---------+------------+-------------
State. | Number | Number | Per cent
| tested. |tuberculous.|tuberculous.
-----------------------+---------+------------+-------------
Alabama | 68,772 | 1,071 | 1.6
Arkansas | 5,917 | 98 | 1.7
Colorado | 1,959 | 76 | 3.9
Connecticut | 29,286 | 4,695 | 16.0
Delaware | 19,003 | 2,132 | 11.2
Florida | 56,533 | 1,438 | 2.5
Georgia | 46,522 | 998 | 2.1
Idaho | 57,731 | 1,052 | 1.8
Illinois | 92,781 | 6,112 | 6.6
Indiana | 142,833 | 3,991 | 2.8
Iowa | 158,514 | 9,958 | 6.3
Kansas | 64,341 | 1,796 | 2.8
Kentucky | 66,839 | 1,492 | 2.2
Louisiana | 36,391 | 981 | 2.7
Maine | 67,406 | 1,792 | 2.7
Maryland | 65,888 | 5,491 | 8.3
Massachusetts | 26,297 | 2,371 | 9.0
Michigan | 163,323 | 5,361 | 3.3
Minnesota | 240,888 | 7,555 | 3.1
Mississippi | 99,245 | 503 | .5
Missouri | 196,208 | 2,587 | 1.3
Montana | 165,640 | 3,346 | 2.0
Nebraska | 125,162 | 3,947 | 3.2
Nevada | 29,541 | 1,042 | 3.5
New Hampshire | 16,623 | 1,697 | 10.2
New Jersey | 32,184 | 2,542 | 7.9
New Mexico | 3,897 | 39 | 1.0
New York | 167,852 | 23,071 | 13.7
North Carolina | 64,008 | 1,098 | 1.7
North Dakota | 139,501 | 4,142 | 3.0
Ohio | 97,612 | 4,470 | 4.6
Oklahoma | 67,522 | 2,453 | 3.6
Oregon | 123,792 | 2,581 | 2.1
Pennsylvania | 102,465 | 6,322 | 6.2
Rhode Island | 3,458 | 338 | 9.8
South Carolina | 41,868 | 740 | 1.8
South Dakota | 43,433 | 2,353 | 5.4
Tennessee | 63,631 | 956 | 1.5
Texas | 61,956 | 1,256 | 2.0
Utah | 59,711 | 586 | 1.0
Vermont | 160,361 | 11,486 | 7.2
Virginia | 135,677 | 3,881 | 2.9
Washington | 154,292 | 3,864 | 2.5
West Virginia | 36,603 | 798 | 2.2
Wisconsin | 285,269 | 8,166 | 2.9
Wyoming | 22,811 | 322 | 1.4
-----------------------+---------+------------+-------------

Reports of tuberculin tests made on 400,000 cattle in the United States during the years 1893 to 1908 by Federal, State, and other officers with tuberculin prepared by the Bureau of Animal Industry show 37,008 reactions, or 9.25 per cent. These were mostly dairy cattle, and in some cases herds were suspected of being diseased.

Later reports of tuberculin tests made in the United States from July 1, 1917, to March 1, 1922, on 3,911,546 cattle by State, county, and Federal officers engaged in cooperative tuberculosis eradication work showed 153,046 reactions, or 3.9 per cent.

All cattle in the District of Columbia, numbering 1,701, were tested with tuberculin in 1909-10, and 18.87 per cent reacted. In 1909-11 herds in Maryland and Virginia supplying milk to the District of Columbia were tested, with 19.03 and 15.38 per cent of reactions, respectively, among 4,501 cattle.

All cattle in the District of Columbia were tuberculin tested in 1920-21, numbering 1,313, and 5 animals reacted, or 0.4 per cent, demonstrating that tuberculosis may be eradicated from all the herds in a circumscribed area.

The beef cattle of the United States show a much smaller proportion of the disease than dairy cattle, though the percentage of cattle found tuberculous in the Government meat-inspection service has increased considerably in recent years. This increase is due partly, but not wholly, to more stringent inspection. Of 7,781,030 adult cattle slaughtered under Federal inspection during the fiscal year ended June 30, 1911, 76,448 were found tuberculous, a percentage of 0.98.

From the statistics above referred to, and other data, it appears that in the more densely populated areas of Europe and America from 5 to 50 per cent of the dairy cattle are more or less affected with tuberculosis, while the proportion of beef cattle affected is distinctly less, ranging from 0.14 to 30 per cent. This difference is due to a number of causes. Beef cattle average younger when slaughtered. They are not so frequently stabled, and are for that reason less liable to infection, and as the males constitute a large proportion of this class of animals the effect of milk secretion in lowering the vital forces is not so apparent. In the United States it has been estimated that about 10 per cent of the dairy cattle are tuberculous, while only about 2 per cent of the beef cattle are so infected.

_Cause and nature of the disease._--The cause of tuberculosis is the tubercle bacillus, which gains entrance to the body, lodges somewhere in the tissues, and begins to grow and multiply at that point. As this bacillus vegetates and increases in numbers it excretes substances which act as irritants and poisons and which lead to the formation of a small nodule, called a tubercle, at the point of irritation. As the bacilli are disseminated through the animal body they affect many parts and cause the formation of an enormous number of tubercles. By the union of such tubercles, masses of tubercular material are formed, which in some cases are of great size. The disease is called tuberculosis because it is characterized by the formation of these peculiar nodules, and the bacillus which causes the disease is for the same reason known technically as the _Mycobacterium tuberculosis._

There are undoubtedly predisposing conditions which contribute toward the development of the disease; some of these are found in the animal body and others in the environment. An enfeebled condition caused by insufficient feed, exposure to great extremes of atmospheric temperature and insanitary surroundings, or the drain occasioned by heavy production of milk, appear to aid the development of the bacillus, and there is also a special individual susceptibility in some cases which may be otherwise described as an inability of the animal tissues to resist and destroy the bacilli when they have penetrated to the inner recesses of the body.

Among the conditions of environment which aid the development of tuberculosis may be mentioned stabling with lack of ventilation, damp buildings, the keeping of many animals together, drafts of air which cause colds and catarrhs, and, in general, everything which prevents the animals from developing and maintaining the highest condition of health. None of these conditions of body or environment are sufficient to cause the disease, however, unless the animals are exposed to the _Mycobacterium tuberculosis_ and it penetrates the tissues of their bodies.

The ways in which the tubercle bacilli find their way into the body may be considered under four heads: (1) By inhalation into the lungs; (2) by taking into the digestive tract in the milk of tuberculous cows or with other contaminated feed; (3) during coition when the sexual organs are tuberculous; (4) from the tuberculous mother to the fetus in the uterus. The bacilli can reach the lungs by inhalation only when the bacilli are thoroughly dried and pulverized and in condition to be carried by currents of air.

It is well known that the bacilli withstand drying for months before they lose their power of producing disease. They leave the bodies of diseased animals in several ways. There may be a little discharge occasionally coughed up as a spray from the diseased lungs, or this material may be swallowed and the bacilli carried off with the excrement, or milk may be spilt, or there may be a discharge from the vagina when the genital organs are tuberculous. There may also be ulcers of the intestines, from which many bacilli escape with the feces. The bacilli from these sources may become dried and pulverized and carried in the air of the stable and into the lungs of still healthy cattle, where the disease then develops.

The disease of the stomach, intestines, and mesenteric glands is very probably the result of feed infection. Tubercle bacilli may have been scattered upon the feed by diseased animals, but the most common source of such infection is the milk of tuberculous cows. Calves may become infected in this way. The disease may remain latent until the animal becomes older. The not-infrequent occurrence of tuberculosis of the uterus and ovaries makes it probable that the disease may be transmitted by a diseased bull or carried by a healthy one from a diseased cow to a number of healthy cows.

The source of infection is always some previous case of the disease, for the disease can never rise spontaneously; hence, in those stables in which there is frequent change of cattle the introduction of tuberculosis by cattle coming from other infected stables is the most frequent source of infection. Since the bacilli when dried can be carried by the air, it is not necessary that healthy animals come in direct contact with cases of disease to become infected. In general, the greatest number of cases occur in the immediate environment of cities, where there are not only abundant opportunities for infection, owing to the frequent introduction of new animals into herds, but where the sanitary conditions may be regarded as the poorest.

The bacillus of tuberculosis was discovered by Robert Koch in 1882. It is a slender, rodlike body (see Pl. XXVIII, fig. 6) from one-third to two-thirds the diameter of a red blood corpuscle in length. As already explained, when the bacillus has become lodged in any organ or tissue it begins to multiply, and thereby causes an irritation in the tissue around it, which leads to the formation of the so-called tubercle. The tubercle, when it has reached its full growth, is a little nodule about the size of a millet seed. It is composed of several kinds of tissue cells. Soon a change takes place within the tubercle. Disintegration begins, and a soft, cheesy substance is formed in the center, which may contain particles of lime salts. When these tubercles continue to form in large numbers they run together, forming masses of various sizes. The disintegration which attacks them leads to the formation of large cheesy masses of a yellowish color, containing more or less of lime salts in the form of gritty particles. These large tuberculous masses are surrounded by or embedded in layers of fibrous tissue which in some cases becomes very dense and thick.

The disease is thus a development of these tubercles in one or more organs of the body. The distribution and number of the tubercles determine the course of the disease.

In a large number of cases the changes are limited to the lungs and the serous membranes[4] of the thorax and abdomen. Pathologists have been in the habit of calling the lung disease tuberculosis and the disease of the serous membranes "pearly disease." Statistics have shown that in about one-half of the cases both lungs and serous membranes are diseased, in one-third only the lungs, and in one-fifth only the serous membranes. At the same time the lymphatic glands near the diseased organs are usually involved. Other organs, such as the liver, not infrequently contain tubercles. Though the disease may remain restricted to a single organ, it now and then is found generalized, affecting all organs of the body.

In the lungs (Pl. XXXIV) the changes observed vary according to the age and intensity of the disease process. They usually begin with the appearance of very minute tubercles. These may appear in large numbers on the surface of the lungs or within the lung tissue. Later the contents become cheesy and partly calcified. When these tubercles are sufficiently numerous to become confluent, large masses may be formed, which undergo the same retrogressive changes of caseation and calcification. In addition to the formation of tubercles in the lung tissue, certain other changes take place. There is usually bronchitis with abundant catarrhal secretion; this plugs up the smaller air tubes, and the lung tissue supplied with air by the tubes collapses. Subsequently it becomes filled with yellowish, cheesy matter, which greatly distends the small air tubes and air vesicles (bronchopneumonia). The connective tissue between the lung lobules, around the tubercles, and around the air tubes becomes thickened and indurated. In the larynx and the bronchi tubercles may vegetate upon the mucous membrane, and ulcers may result from their breaking down. The inflammatory irritation which the growth of the tubercles on the surface of the lungs arouses gives rise to adhesion of the lungs to the ribs and diaphragm. This adhesion is sometimes so firm and extensive that the lungs appear grown to the chest wall.

When, therefore, the lungs in advanced stages of the disease are cut open we observe large yellowish masses, from one-quarter to three-quarters of an inch in diameter, of a cheesy texture, in which calcified, gritty particles are embedded and which are surrounded by very firm connective tissue. The neighboring lung tissue, when collapsed and involved in bronchopneumonia, has the color and consistency of pale-red flesh. The air tubes, large and small, stand out prominently on the cut surface. They are distended with a pasty, yellowish, cheesy mass, surrounded and enveloped in thick mucus, and their walls greatly thickened. The larger bronchi may be sacculated, owing to the distention produced by the cheesy contents.

The disease usually attacks the bronchial glands, which are situated on the trachea and bronchial tubes at the bifurcation. The changes in the glands are the same as those going on in the lung tissue, and they frequently reach an enormous size.

The tubercle formation on the serous membranes covering the lungs and chest wall (Pl. XXXVII, fig. 2), which may go on at the same time with the lung disease or independent of it, has been called "pearly disease," on account of the peculiar appearance of the tubercles. These begin as very minute, grayish nodules, which give the originally smooth, lustrous membrane a roughened appearance. These minute tubercles enlarge, become confluent, and project above the surface of the membrane as wartlike masses, attaining the size of peas. In this stage their attachment to the membrane is by means of delicate fibers. The attachment is loose, so that the tubercle hangs by a short pedicle or neck and may be moved slightly to and fro. Large masses are frequently formed by a coalescence of many tubercles and the secondary formation of the same. These may be found on the lungs, the ribs, and the diaphragm. These tubercles likewise undergo degenerative changes. The center partly softens and partly calcifies into a grayish mortarlike mass, and is gritty. Associated with the formation of tubercles on the pleura, those glands situated back of the center of the lungs between the two main lobes (posterior mediastinal) become greatly enlarged and the center cheesy. (Pl. XXXVI, fig. 1.) They may compress the esophagus and interfere with swallowing. The size attained by these tumors and new growths is well illustrated by the fact that, taken together, they not infrequently weigh from 60 to 80 pounds. The bronchial glands, which in the healthy state are not so large as horse-chestnuts, have been found to attain a weight of more than 10 pounds.

In the abdominal cavity tubercles may be found, both in the organs and on the serous membranes covering them. They are situated usually on the omentum, or caul (see Pl. XXXVI, fig. 2), the diaphragm, and the walls of the abdomen. In the liver large and small tubercular masses are occasionally encountered. (See Pl. XXXV.) The mesenteric glands are occasionally enlarged and tuberculous; likewise the glands near the liver. Tubercles may also develop in the spleen, the kidneys, the uterus and ovaries, and the testicles.

Tubercular affection of the intestines seems to be quite rare, although ulcers of the large intestines have been observed. Nodules may also form under the serous covering of the intestines.

The brain and spinal cord are occasionally found tuberculous. Of 40 cases, Semmer found tuberculosis of the brain in 4. It is not improbable that, owing to the infrequency of exposing the brain and spinal cord, tuberculosis may have escaped the attention of pathologists, and it may be that it is not so uncommon as is generally supposed. The tubercles occur on the membranes of the brain as well as in the substance of the brain itself. They project into the ventricles as masses, varying in size from a pinhead to a hen's egg. They finally lead to various inflammatory changes. Jˆhne has observed numerous small tubercles on the membranes of the spinal cord.

Very rarely tuberculous lesions have been observed in the bones and muscles of the body. Not so rare, however, is the affection of the lymphatic glands embedded in the muscular tissue, and those which can be felt beneath the skin. These are situated at the joints, under the jaw, and along the neck.

Of late tubercular disease of the udder in cows (Pl. XXXVIII) has received considerable attention from sanitarians, owing to the infection of the milk with the virus of tuberculosis. According to those who have given this subject special attention, the udder becomes swollen uniformly and quite firm. This swelling, which is painless, frequently attacks but one quarter, more rarely two, these being usually the hind quarters. The larger milk ducts contain yellowish, cheesy particles, in which are many tubercle bacilli. Later larger nodules can be felt within the udder, which undergo the various changes to which tubercles are subject. The udder may grow very hard to the touch and become very large, weighing in some cases up to 40 pounds. The milk, at first normal, becomes thin and watery after a month or so, and is mixed with flakes and tubercle bacilli.

As regards the frequency of the tuberculous processes in the different organs, the following carefully compiled statistics of the disease in Bavaria and Baden may serve as a guide:

Bavaria: Per cent.
Tuberculosis of lungs and serous membranes 41
Tuberculosis of lungs alone 33
Tuberculosis of serous membranes alone (pearly disease) 17
Tuberculosis of other organs 8

Baden:
Tuberculosis of lungs alone 21
Tuberculosis of serous membranes alone 28
Both combined 39
Generalized tuberculosis 9
Tuberculosis of the sexual organs alone 3

_Symptoms._--The beginning of the disease usually passes unnoticed, inasmuch as it is very slow and insidious and rarely accompanied with fever. When the lungs are involved a dull, short cough is noticed, which may later on become prolonged, convulsive, and very troublesome to the animal. The cough is more frequent in the morning after movement and drinking. The breathing varies. Only when much of the lung tissue is diseased is it labored and accompanied with active movements of the chest and nostrils. Discharge from the nose is rare or absent. At times, however, when the tubercles have broken down and cavities containing cheesy masses have formed in the lung tissue, or when the air tubes have become filled with cheesy and mucous masses, coughing will dislodge them and cause their discharge. In advanced stages the breath may have a disagreeable odor. Pressure on the chest wall may give rise to pain.

The general effect on the body is at first slight. In fact, animals may remain in good flesh for a considerable time. Invariably as the disease progresses loss of flesh and appetite and paleness of the mucous membranes become manifest. These symptoms are accompanied with a gradual diminution of the milk secretion. The debilitated condition of the animal is also manifested by a staring coat and a tough, dry, harsh skin (hidebound). Digestive disturbances are indicated by tympanites, or distention of the rumen by gas, colic, and diarrhea, alternating with constipation. The animal generally dies from exhaustion after a period of sickness which may last months or even years.

* * * * *

TUBERCULOSIS. DESCRIPTION OF PLATES.

PLATE XXXIV. Tuberculosis of the lungs of cattle. The upper figure represents a large cheesy mass, surrounded by a capsule of connective tissue, the whole embedded in healthy lung tissue. The lower figure illustrates in section a mass of tubercles which have undergone cheesy degeneration, and some of which are surrounded by dense connective tissue.

PLATE XXXV. Tuberculosis of the liver. A large portion of the lobe represented in the plate has undergone tuberculous changes. Numerous nodules are shown in various stages of the disease, the majority of which, however, contain the yellowish, partly cheesy, partly gritty areas characteristic of advanced tuberculous degeneration. This large mass involves the surface of the liver, and also extends into the liver substance.

PLATE XXXVI. Tuberculosis of lymph gland and of omentum (caul).

Fig. 1. A lymph gland from the region of the thorax behind or above the esophagus, or gullet (posterior, or dorsal, mediastinum). The gland is shown cut through and laid open. It is very much enlarged, and the yellowish cheesy masses which represent tissue undergoing tuberculous changes are well shown on the cut surface.

Fig. 2. Omentum, or caul, resting upon the paunch. The reddish nodules with which the membrane is beset are tubercles, the product of the disease.

PLATE XXXVII. Fig. 1. Tuberculosis of the sirloin and porterhouse cuts of beef. The grapelike tuberculous growths are mainly restricted to the lining membrane of the abdomen.

Fig. 2. Tuberculosis of the pleura of a cow, so-called "pearly disease." Notice the grapelike clusters of tubercular nodules scattered over the lining membrane of the chest (pleura).

PLATE XXXVIII. Tuberculosis of cow's udder. The udder was uniformly swollen and quite firm. Small cheesy foci and yellowish lines of tuberculous material follow the course of the milk ducts. The mucous membrane of the milk cistern (_a_) is ulcerated and covered with yellowish cheesy particles. The supramammary lymphatic gland (_b_) is greatly enlarged and contains many miliary tubercular foci.

* * * * *

Tuberculosis in the abdominal organs is often signalized by abortion and by abnormal sexual manifestations. When the brain is involved, the disease may cause convulsions, unconsciousness, paralysis, as well as peculiar movements in a circle, oblique position of the head, etc. Lydtin quotes the following description of the disease as taken from a Swiss sanitary order:

A dry, short, interrupted, hoarse cough, which the sick animals
manifest, especially in the morning at feeding time, still more after
somewhat violent exertion. At first these animals may be full blooded
and lay on a considerable amount of fat when well fed. As the disease
progresses they grow thin and show more and more those appearances which
indicate diseased nutrition, such as a staring, lusterless, disheveled
coat; dirty, tense skin, which appears very pale in those regions free
from hair. The temperature of the skin is below normal. The loss of fat
causes sinking of the eyes in their sockets. They appear swimming in
water, and their expression is weak. The cough is more frequent, but
never or very rarely accompanied with discharge. The body continues to
emaciate, even with plenty of food and a good appetite, so that the
quantity of milk is small. At times in the early stages of the disease,
still more in the later stages, the diseased animals manifest
considerable tenderness when pressure is applied to the front or the
sides of the chest by coughing, moaning, etc. Often symptoms are wanting
in spite of the existence of the disease.

Lydtin also quotes at length a description of the abnormal sexual desire occasionally observed among cows when affected with this disease.

_Diagnosis._--A disease so varied in its attack upon the different organs of the body and in the extent of the disease process must necessarily lead to mistakes when diagnosis is attempted by ordinary means of examination. It has been confounded with the later stages of pleuropneumonia, with parasitic diseases of the brain, the lungs, the intestines, and with actinomycosis. A careful examination of the lungs by auscultation and percussion enables the expert to locate large tuberculous masses, owing to dullness, loss of respiratory murmur, and abnormal sounds, such as blowing, whistling, and creaking. The majority of cases of tuberculosis in cattle, however, including many in which the lungs are quite seriously involved, can not be detected in this manner.

THE TUBERCULIN TEST.

The tuberculin test, which is marvelously accurate in its indications, has been almost universally adopted for the detection of tuberculosis. Tuberculin is a drug prepared by sterilizing, filtering, and concentrating the liquids in which the tubercle bacillus has been allowed to vegetate. It contains the cooked products of the growth of these bacilli, but no living bacilli; consequently, when this substance is injected under the skin of an animal it is absolutely unable to produce the disease, cause abortion, or otherwise injure the animal. In case the injected animal is normal there is no more effect upon the system than would be expected from the injection of sterile water; however, if the animal is tuberculous, a decided rise of temperature will follow the use of tuberculin by the subcutaneous method. This substance, discovered by Koch, has the effect, when injected into the tissues of a tuberculous animal, of causing a decided rise of temperature or other manifestations while it has no such effect upon animals free from the disease. The value of tuberculin for this purpose was tested during the years 1890 and 1891 by Guttman, Roeckl and Sch¸tz, Bang and Salomonsen, Lydtin, Jˆhne and Siedamgrotzky, Nocard, and many others. It was at once recognized as a most remarkable and accurate method of detecting tuberculosis even in the early stages and when the disease had yet made but little progress. It is now quite generally employed.

The tuberculin test came into existence through the most careful and thorough scientific experimentation.

As a result of its use an accurate diagnosis may be established in more than 90 per cent of the cases tested. The relatively few failures in diagnoses are included among two classes of cattle. The first class contains those that are tuberculous, but which do not react either because of the slight effect of an ordinary-sized dose of tuberculin on an advanced case of the disease with so much natural tuberculin already in the system, or on account of a recent previous test with tuberculin which produces a tolerance to this material, lasting for about six weeks. The second class includes those that are not tuberculous, but which show indications of a reaction as a result of (_a_) advanced pregnancy, (_b_) the excitement of [oe]strum, (_c_) concurrent diseases, as inflammation of the lungs, intestines, uterus, udder, or other parts, abortion, retention of afterbirth, indigestion, etc., (_d_) inclosure in a hot, stuffy stable, especially in summer, or exposure to cold drafts or rains, (_e_) any change in the method of feeding, watering, or stabling of the animal during the test. Notwithstanding all these possibilities of error, the results of thousands of tests show that in less than 3 per cent of the cases tested do these failures actually occur. In the first class the chances of error are decidedly reduced by the skilled veterinarian by making careful physical examination and diagnosing clinically these advanced cases, and by the injection of double or triple doses into all recently tested cattle, with the taking of the after-temperature, beginning two hours following the injection and continuing hourly for 20 hours.

It is therefore apparent that tuberculin should be applied only by or under the direction of a competent veterinarian, capable not only of injecting the tuberculin but also of interpreting the results, and particularly of picking out all clinical cases by physical examination. The latter observation is extremely important and should always be made on every animal tested.

In the second class, where the temperature test is used, errors are avoided by eliminating from the test those cases that are nearing parturition or are in heat or show evidence of the previously mentioned diseases or exhibit temperatures sufficiently high to make them unreliable for use as normal. Where other methods of test are used these conditions do not have an important bearing on the results. In addition, a satisfactory tuberculin must be used; also an accurate thermometer and a reliable syringe, in order that a sufficient dose of tuberculin may be given. Finally, the number of apparent errors of the tuberculin test will be greatly diminished if a careful post-mortem examination is made, giving especial attention to the lymph glands. This low percentage of failures being the case, cattle owners should welcome the tuberculin test, not only for their own interest but for the welfare of the public as well. Where this method of diagnosing the disease has been adopted tuberculosis is gradually being eradicated. Without its use the disease can not be controlled and the owner is confronted with serious and continuous losses; with its use the disease can be eradicated from the herd, a clean herd established in a few years without very serious loss or hardship, and the danger of its spread to man removed. Tuberculin may therefore be considered a most beneficial discovery for the stock raiser.

Law has clearly stated the question when he says--

Many stock owners still entertain an ignorant and unwarranted dread of
the tuberculin test. It is true that when recklessly used by ignorant and
careless people it may be made a root of evil, yet as employed by the
intelligent and careful expert it is not only perfectly safe, but it is
the only known means of ascertaining approximately the actual number
affected in a given herd. In most infected herds living under what are in
other respects good hygienic conditions two-thirds or three-fourths are
not to be detected without its aid, so that in clearing a herd from
tuberculosis and placing both herd and products above suspicion the test
becomes essential. * * * In skilled hands the tuberculin test will show
at least nine-tenths of all cases of tuberculosis when other methods of
diagnosis will not detect one-tenth.

Probably the most popular objection to tuberculin is that it is too searching, since it discovers cases in which the lesions are small and obscure. While this fact is admitted, it should also be remembered that such a small lesion to-day may break down and become widely disseminated in a relatively short period. Therefore any cow affected with tuberculosis, even to a slight degree, must be considered as dangerous not only to the other animals in the herd but also to the consumer of her products.

In 1898 Bang, of Copenhagen, one of the highest European authorities, in his paper presented to the Congress for the Study of Human and Animal Tuberculosis, at Paris, said:

Numerous tests made in almost every civilized country have demonstrated
that in the majority of cases tuberculin is an excellent means for
diagnosing the existence or nonexistence of the disease, but giving us no
positive information as to the extent to which the disease has
progressed. When tuberculin produces a typical reaction we may be
almost sure that there exists in the body of the animal a tubercular
process. The cases in which a careful examiner has not succeeded in
finding it are very rare, and I am led to believe that when,
notwithstanding all the pains taken, it has escaped discovery, the reason
is that it is located in a portion of the body that is particularly
inaccessible. Nevertheless, it is not to be denied that a fever, entirely
accidental and of short duration, may in some rare cases have simulated a
reaction. However this may be, the error committed in wrongly condemning
an occasional animal for tuberculosis is of no practical consequence.

A worse aspect of the case is that there are some diseased animals in
which tuberculin fails to discover the existence of tuberculosis. In
most of these, no doubt, the deposits are old, insignificant, and
generally calcified, or they are cases where the disease is arrested and
perhaps in process of recovery, and which are possibly incapable of
disseminating the contagion. But it is known that there are cases, not
altogether rare, where tuberculin fails to cause a reaction in a highly
tuberculous animal, and consequently one in which the disease exists in
an extremely contagious form. For this reason a clinical examination
should always be made of an animal which does not give a reaction but
which shows symptoms indicating that, notwithstanding the test, it may
suffer from tuberculosis.

Nocard, of Paris, wrote also in 1898 as follows:

The degree of certainty of the indications furnished may be stated in
precise terms. _The observation of a clear reaction to tuberculin is
unequivocal; the animal is tuberculous._ The pretended errors imputed to
the method are explained by the extreme sensitiveness of the reagent,
which is capable of detecting the smallest lesion. It often requires
prolonged and minute researches in the depths of all the tissues to
discover the few miliary centers, the presence of which has been
revealed. The reaction is absolutely specific. In those cases where it is
observed with animals which show lesions of another disease
(actinomycosis, hydatid disease, verminous bronchitis, distomatosis), it
may be affirmed that there exists, in addition to these conspicuous
changes, a tuberculous center which alone has provoked the reaction.

_The failure to react does not necessarily imply absence of
tuberculosis._ Such failures of tuberculin are very exceptional. They are
seen most frequently with animals affected with tuberculosis in a very
advanced stage and made evident by plain external signs. Sometimes, also,
there are found at the post-mortem examination of animals which have not
reacted small fibrous or calcified lesions in such a condition that one
is tempted to believe them cured. Whether sterile or not, these lesions
have no tendency to increase, and they are not very dangerous from the
point of view of contagion.

These opinions of two eminent authorities, living in different countries, after long experience of their own and after studying the results of the many tests made in different parts of the world, should have great weight. They are essentially the same throughout.

In 1897 Voges compiled statistics of tuberculin tests, the accuracy of which had been determined by post-mortem examination. Of 7,327 animals tested, it appeared that errors had been made with 204, or 2.78 per cent. In the work of the Pennsylvania Live Stock Sanitary Board post-mortem examinations were made on about 4,400 reacting cattle and the disease was found in all but 8 of those which had given characteristic reactions.

The results of a much larger number of tests might be compiled at this time, but they would not materially change the average of those already mentioned. It is plain that tuberculin is a remarkably accurate test of tuberculosis, that the animals which react may be safely considered as tuberculous, and that when a careful clinical examination is practiced in addition to the test there are few animals in a dangerous condition which escape detection.

The first questions asked by those who oppose the adoption of the tuberculin tests are: Is this test infallible? and, if it is not infallible, why should it be forced upon the cattle owners of the country?

In answer to these questions it may be said that tuberculin is not absolutely infallible, and yet it is by far the best method of diagnosing tuberculosis that has been discovered. It is much better than any test known for pleuropneumonia when that disease was eradicated.

Practically all the animals that react are affected with tuberculosis and should be separated from the herd, not only in the interest of the public, but in the interest of the owner of the herd. The best authorities admit, after studying many thousands of tests, that there are few, if any, mistakes made in condemning cattle which show a typical tuberculin reaction. The errors are principally in the other direction--that is, some tuberculous animals are not discovered by the tuberculin test, but as the most dangerous of these may be picked out by ordinary clinical examination this fault of tuberculin is not so serious as it at first sight appears. This being the case, it should not be necessary to force the tuberculin test upon owners. They should be anxious to adopt it in their own interests and for the protection of their patrons. There is to-day no greater danger to the cattle and hog industries than that which confronts them in the form of tuberculosis, a disease already widespread and rapidly extending. Furthermore, in view of the results revealed by numerous tests covering vast numbers of animals, tuberculin must be considered as harmless for healthy animals. It has also been clearly demonstrated that tuberculin interferes in no way with the milking function in healthy cattle; neither in the quantity of milk nor in butter-fat value has any variation been detected. The conclusions of some of the best authorities on the subject of its harmlessness to healthy animals are given below.

Nocard and Leclainche state:

Direct experiments and observations collected by thousands show that the
tuberculin injections have no unfavorable effect. With healthy animals
the system is indifferent to the inoculation; with tuberculous animals it
causes slight changes which are not at all serious.

Bang has written as follows on this question:

We will now consider the following question, a very important one, in the
application of tuberculin, viz: Can the reaction produce a worse
condition in tuberculous animals than before existed? Hess emphatically
states that it can, and on this account he earnestly warns against its
application. My attention has been directed to this question from the
beginning. In my first publication on tuberculin injection I reported two
cases in which acute miliary tuberculosis was proved in two high-grade
tuberculous cows several weeks after the tuberculin injection. I then
stated my suspicion that perhaps the tuberculin injection had some
connection with this, just as is often supposed to be the case in human
practice. With my present very large amount of material for observation
at hand I may express the following opinion: Such an acute development of
tuberculosis as a result of tuberculin injection is to be feared only
exceptionally, and then in cases of advanced tuberculosis. _It must not
be forgotten that acute miliary tuberculosis by no means rarely
accompanies an advanced tuberculosis of long standing._ It is therefore
impossible to offer strict proof of the causal connection with the
injection, and only oft-repeated observation could make this probable.
In support of my view I offer the following: In the course of the last
three years I have made careful post-mortem examinations of 83
tuberculous animals, which have been removed from my experiment farm,
Thurebylille. Among these were 18 (or, strictly speaking, 23) high-grade
tuberculous animals. I have been able to prove miliary tuberculosis in
only 4 of these. Among the others, which showed less developed
tuberculosis, I have never found miliary tuberculosis, and with very many
I have never found any sign of a more rapid development of the process.
On the contrary, it has been proved that the disease was restricted
locally, often for years, in spite of yearly repeated injections.
Dissections were made at very different periods after the injections--in
17 cases from 4 to 12 days after the last test. In all of these cases
earlier tests had been made months or years before. In 28 cases the
injection took place from 19 days to 2 months before the butchering; in 3
of these cases earlier injections had been made. In 38 cases from two and
one-half months to one year intervened between the last injection and the
dissection. Dissection gives the best explanation of this question, but a
clinical observation, continued for years, of a herd tested with
tuberculin can render very essential aid. If Hess's opinion is correct,
it is to be assumed that tuberculosis must take an unusually vicious
course in such herds, but this I have been unable to prove. At
Thurebylille there has existed for three years a reacting division,
consisting originally of 131 head and now 69. Although these animals are
yearly tested, and although most of them react every year, the division
certainly appears to be made up of healthy animals, and the farm
inspector has expressed the decided opinion that the tuberculosis in this
division is no more developed than at the beginning of the experiment.
The testimony of many owners of large herds of cattle which have long ago
been injected is to the same effect. I will adduce statements from
several. A farm tenant whose cattle were injected 20 months previously,
when 82 per cent of the grown animals reacted, wrote me recently as
follows: "Only 2 cows from the division of 100 head had been sold as
decidedly tuberculous. The majority appeared afterwards, just as before,
entirely healthy. The fat animals which had been slaughtered had been
pronounced healthy by the butchers." Another farm tenant with a herd
injected in 1894 had not been obliged to remove a single animal from the
tuberculosis division, numbering 70 head. A large farm owner in Jutland
stated in September that he had traced no undesirable result from the
injection. His herd of 350 had been injected in February and about 75 per
cent reacted. Similar answers have been given by other owners and
veterinarians.

A veterinarian who had injected 600 animals, among them a herd of a large
farm, 18 months previously, expressed the belief that the injection had
produced in no single case an unusually rapid or vicious course of
tuberculosis. In spite of a demand made months ago, I have received thus
far no report from any veterinarian of an undesirable result.

On a large farm, on which before the injection tuberculosis had appeared
in a vicious form, the owner had the impression that the severe cases had
afterwards become more numerous. He had, however, not suffered severe
losses, and 8 months later the large reacting division by no means made a
bad impression. Finally, it is to be noticed that tuberculin has been
employed on a large scale in Denmark for years, and still the demand from
farmers constantly increases. This could certainly not be the case if the
injections were generally followed by bad results.

Paige said, after the tests of the herd of the Massachusetts Agricultural College, that "its use is not followed by any ill effects of a serious or permanent nature."

Lamson, of the New Hampshire College Agricultural Experiment Station, said: "There is abundant testimony that its use is not in any way injurious to a healthy animal."

Conn, who made a special study of the present attitude of European science toward tuberculosis in cattle, reached the following conclusions:

It has been, from the first, thought by some that the use of tuberculin
produces a direct injury upon the inoculated animals. This, however, is
undoubtedly a mistake, and there is no longer any belief anywhere on the
part of scientists that the injury thus produced is worthy of note. In
the first place, the idea that it may produce the disease in a perfectly
healthy animal by the inoculation is absolutely fallacious. The
tuberculin does not contain the tubercle bacillus, and it is absolutely
certain that it is impossible to produce a case of tuberculosis in an
animal unless the tubercle bacilli are present. The use of tuberculin,
therefore, certainly can never produce the disease in the inoculated
animal.

It has been more widely believed, however, that the inoculation of an
animal with this material has a tendency to stimulate an incipient case
of tuberculosis. It has been thought that an animal with a very slight
case of the disease may, after inoculation, show a very rapid extension
of this disease and be speedily brought to a condition where it is
beyond any use. The reasons given for this have been the apparent
activity of the tuberculosis infection in animals that have been
slaughtered shortly after inoculation. This has been claimed, not only
by agriculturists who have not understood the subject well, but also by
veterinarians and bacteriologists. But here, too, we must recognize that
the claim has been disproved, and that there is now a practical
unanimity of opinion on the part of all who are best calculated to judge
that such an injurious effect does not occur. Even those who have been
most pronounced in the claim that there is injury thus resulting from
tuberculin have, little by little, modified their claim, until at the
present time they say either that the injury which they formerly claimed
does not occur or that the stimulus of the disease is so slight that it
should be absolutely neglected in view of the great value which may
arise from the use of tuberculin. Apart from two or three who hold this
very moderate opinion, all bacteriologists and veterinarians unite in
agreeing that there is no evidence for believing that any injury
results. In Denmark, especially, many hundreds of thousands of animals
have been inoculated, and the veterinarians say there is absolutely no
reason in all their experience for believing that the tuberculin
inoculation is followed by any injurious results.

In 1898 tuberculosis was found in the large Shorthorn herd belonging to W. C. Edwards, of Canada, who with commendable promptness and public spirit had his animals tested, and at once proceeded to separate the diseased from the healthy animals. They were all finely bred animals, and of the very class which we have been told are most susceptible to the injurious effects of tuberculin. After using this test regularly for two years, Mr. Edwards wrote as follows:

I have seen nothing to lead me to believe that the tuberculin test had
any injurious influence on the course of the disease. It is by no means
our opinion that the disease has been stimulated or aggravated by the
application of the tuberculin test. All animals that we have tested two
or three times continue as hale and hearty as they were previously, and
not one animal in our herds has broken down or failed in any way since
we began testing.

Mr. Edwards, in December, 1901, verbally stated that his views as to the harmlessness of tuberculin remained unchanged, and that he had not seen the least ill effect in any of his cattle from its use.

Those who have had most experience with tuberculin have failed to observe any injurious effects following its use upon healthy cattle. With tuberculous cattle it produces a fever of short duration, and in the great majority of cases all derangement of the system which it causes disappears within 48 hours after the tuberculin is administered. There appear to have been a very few cases in which the disease was aggravated, and a greater number in which it was benefited by the injection of tuberculin. The cases of abortion following the tuberculin test have not been numerous, even when cows were tested within a few weeks of the normal time of calving. The few cases of this kind which have occurred may be explained by the fact that abortion in cattle is a very common occurrence, and that it would inevitably happen sometimes after the tuberculin test as a mere coincidence and without any relation between the test and the loss of the calf. The cases of abortion which have been cited appear to be no more numerous than might be expected to have occurred among the same number of cattle within the same period if the test had not been applied.

At the present time there is ample evidence to show that tuberculin is the most reliable means of detecting tuberculosis in the living animal and that its use is not attended by any harmful aftereffects.

An act of Congress was approved July 24, 1919, for the purpose of controlling and eradicating tuberculosis of animals. The official means of detecting tuberculosis in the living animal is the tuberculin test, which may be applied by three different methods--the subcutaneous, the intradermic, and the ophthalmic. It is not necessary to discuss here the details of these three methods, which are made use of in the work of eradication of tuberculosis.

The plan adopted by the State and Federal authorities in eradication of the disease is known as "The Accredited-Herd Plan." Under this plan herds are tested under State and Federal supervision, the diseased animals are appraised, removed, and slaughtered under Federal inspection. Retests are then made after definite periods of time until two successive tests show all the animals to be free from the disease. At this time the herd owner is given a certificate of an accredited herd.

Details concerning the accredited-herd plan may be obtained by applying to the Chief of the Bureau of Animal Industry, Washington, D. C.

THE TUBERCULIN TESTS.

Testing animals with tuberculin is the process of introducing tuberculin into the animal and interpreting results according to well-known standards.

From the investigations and observations that have been mentioned, it may be safely concluded--

1. That the tuberculin test is a wonderfully accurate method of determining whether an animal is affected with tuberculosis.

2. That by its use the animals diseased with tuberculosis may be detected and removed from the herd, thereby eradicating the disease.

3. That it has no injurious effect upon healthy cattle.

4. That the comparatively small number of cattle which have aborted, suffered in health, or fallen off in condition after the test were either diseased before it was made or were affected by some cause other than the tuberculin.

THE SUBCUTANEOUS TEST (UNDER THE SKIN).

The most frequently used method of testing is the subcutaneous test, which consists in injecting the proper quantity of tuberculin underneath the skin into the subcutaneous tissue. If an animal is tuberculous, the action of the tuberculin causes a fever, which is indicated by a rise in temperature. This rise, under ordinary conditions, may occur any time between the eighth and twentieth hours after the tuberculin is injected, but in some cases it is desirable to measure the temperature before the eighth hour and continue to the twenty-fourth hour or longer.