Chapter XVII: Appendix

It is proposed to add one or two notes on certain technical points in bacteriological work, with a view to assisting those medical men not able to obtain the advantages of a well-equipped laboratory, and yet desirous of occasionally attempting some practical bacteriology.

1. _General Examination._ All fluids may be examined for bacteria in two chief ways:

(_a_) A small quantity may be placed on a cover-glass or slide, dried over a lamp or bunsen flame, and stained with aniline dyes for a few minutes. It is then ready for microscopic examination. It is obvious that the result will generally be a _mixture_ of bacteria, for which differentiating stains may be used (Gram, Ziehl-Neelsen, etc.).

(_b_) A minute drop of the suspected fluid may be added to various fluid media (broth, liquefied gelatine, etc.) and then plated out upon small sterilised sheets of glass. In the course of two or three days the contained bacteria will reveal themselves in characteristic colonies, which may be examined, and if possible sub-cultured, and carefully studied.

_Double-Staining Methods._ These are various, and are used when it is desired to stain the bacteria themselves one colour, and the matrix or ground substance in which they are situated another colour. Three of the commoner methods are those of Ehrlich, Neelsen, and Gram. They are as follows:

_Ehrlich's Method._ "Five parts of aniline oil are shaken up with 100 parts distilled water, and the emulsion filtered through moistened filter paper. A saturated alcoholic solution of fuchsine, methyl-violet, or gentian-violet is added to the filtrate in a watch-glass, drop by drop, until precipitation commences. Cover-glass preparations are floated in this mixture for fifteen to thirty minutes, then washed for a few seconds in dilute nitric acid (one part nitric acid to two of water), and then rinsed in distilled water. The stain is removed from everything except the bacilli; but the ground substance can be after-stained brown if the bacilli are violet, or blue if they have been stained red" (Crookshank, _Bacteriology and Infective Diseases_, p. 89).

_Gram's Method._ The primary stain in this method is a solution of aniline gentian-violet (saturated alcoholic solution of gentian-violet 30 cc., aniline water 100 cc.), which stains both ground substance and bacteria in purple. The preparation is next immersed in the following solution for half a minute or a little more:

Iodine 1 part
Potassium iodide 2 parts
Distilled water 300 parts

In this short space of time the iodine solution acts as a mordant of the purple colour in the bacteria, but not in the ground substance. Hence, if the preparation be now (when it has assumed a _brown_ colour) washed in alcohol (methylated spirit), the ground substance slowly loses its colour and becomes clear. But the bacteria retain their colour, and thus stand out in a well-defined manner. Cover-glass preparations decolourise more quickly than sections of hardened tissue, and they should only be left in the methylated spirit until no more colour comes away. The preparation may now be washed in water, dried, and mounted for microscopic examination, or it may be double-stained, that is, immersed in some contrast colour which will lightly stain the ground substance. Eosin or Bismarck brown are commonly used for this purpose. The former is applied for a minute or two, the latter for five minutes, after which the specimen is passed through methylated spirit (and preferably xylol also) and mounted. The result is that the bacteria appear in a dark purple colour on a background of faint pink or brown. Carbol-thionine blue, picro-carmine, and other stains are occasionally used in place of the aniline gentian-violet, and there are other slight modifications of the method.

_Ziehl-Neelsen Method._ Here the primary stain is a solution of carbol-fuchsin:

Fuchsin 1 part
Absolute alcohol 10 parts
5 per cent. aqueous solution of carbolic acid 100 parts

It is best to heat the dye in a sand-bath, in order to distribute the heat evenly. The various stages in the staining process are as follows: (_a_) The cover-glass with the dried film upon it is immersed in the hot stain for one to three minutes. (_b_) Remove the cover-glass from the carbol-fuchsin, and place it in a capsule containing a 25 per cent. solution of sulphuric acid to decolourise it. Here its redness is changed into a slate-grey colour. (_c_) Wash in water, and alternately in the acid and water, until it is of a faint pink colour. (_d_) Now place the cover-glass for a minute or two in a saturated aqueous solution of methylene-blue, which will counter-stain the decolourised ground substance blue. (_e_) Wash in water. (_f_) Dehydrate by rinsing in methylated spirit, dry, and mount. A pure culture of bacteria will not necessarily require the counter-stain (methylene-blue). Sections of tissue may require twenty to thirty minutes in the primary stain (carbol-fuchsin). This stain is used for tubercle and leprosy. With a little practice the staining of the bacillus of tubercle when present in pus or sputum becomes a very simple and accurate method of diagnosis. A small particle of sputum or pus is placed between two clean cover-glasses and thus pressed between the thumb and finger into a thin film. This is readily dried and stained as above, the bacillus of tubercle appearing as a delicately-beaded red rod with a background of blue.

_Bacteriological Diagnosis._ The following points must be ascertained in order to identify any particular micro-organism:

(1) Its morphology, bacillus, coccus, spirillum, etc.; the presence or absence of involution forms.

(2) Motility by the unstained cover-glass preparation ("hanging drop"); note presence of flagella.

(3) Presence of spores, their appearance and position.

(4) Whether or not the organism stains with Gram's method.

(5) The character of the growth upon various media (gelatine, agar, milk, potato, broth); the presence or absence of liquefaction in the gelatine culture; its power of producing acid, gas, or indol.

(6) Whether it is aërobic or anaërobic.

(7) Its colour in cultivation.

(8) If it is a disease-producing organism under examination, its effect upon the animal tissues and the course of the disease should be observed.

There are other points of importance, but the above are essential to a right conclusion.

_Diagnosis in Special Diseases:_

(1) _Diphtheria._ This disease may be bacteriologically diagnosed with a minimum of apparatus and equipment. By means of a swab a rubbing from a suspected throat is readily obtained. This may be examined by the microscope, or sub-cultured on favourable medium. Blood serum is perhaps the best, but, as Hewlett remarks, "If no serum tubes can be had, an egg may be used. It is boiled hard, the shell chipped away from one end with a knife sterilised by heating, and the inoculation made on the exposed white surface; the egg is then placed, inoculated end down, in a wine-glass of such a size that it rests on the rim and does not touch the bottom. A few drops of water may with advantage be put at the bottom of the glass to keep the egg-white moist. The preparation is kept in a warm place for twenty-four to forty-eight hours and then examined." The examination, of course, consists in staining and preparing for the microscope and observing the form, arrangement, and characters of the organism or organisms present. A small piece of the membrane may be detached, washed in water, and stained for the bacilli.

(2) _Tubercle_ (Ziehl-Neelsen's stain, _vide supra_).

(3) _Typhoid_ (_Enteric Fever_).

_Widal's Reaction._ This diagnostic test depends upon the effect which the blood of a person suffering from typhoid fever has upon the _Bacillus typhosus_. The effect is twofold. In the first place, the actively motile _B. typhosus_ becomes immotile; and secondly, there is an agglutination, or grouping together in colonies, of the _B. typhosus_. Neither of these features occurs if healthy human blood is brought into contact with a culture of the typhoid bacillus. There are various ways in which this "serum diagnosis" can be carried out. The simplest and quickest method is as follows: To ten drops of a twenty-four or forty-eight-hours-old neutral broth culture of the typhoid bacillus one drop of the blood serum to be tested is added. The serum and culture are rapidly mixed in the trough of a hollow ground slide (such as is used for the "hanging drop"), and a single drop is taken, placed upon an ordinary clean slide, and a cover-glass superimposed. The positive reaction of agglutination and immotility, if the blood comes from a case of typhoid fever, will probably appear within fifteen or twenty minutes. The fluid culture of typhoid may be taken from an agar culture as well as from broth. In both cases it may be desirable to filter through ordinary filter paper to remove any normally agglutinated masses of bacilli before commencing the test.

In his first experiments Widal used a test-tube in the following manner: The blood to be tested is diluted by one part of it being added to fifteen parts of broth in a test-tube. The mixture is inoculated with a drop of a typical _Bacillus typhosus_ culture. The tube is then incubated at 37° C. for twenty-four hours, after which it is examined. If the reaction be positive, the broth appears comparatively clear, but at the bottom of the test-tube a more or less abundant sediment will be found. This is due to the clumps of bacilli having fallen owing to gravity. If, on the other hand, the reaction is negative, the broth will appear more or less uniformly turbid.

For the _apparatus_ required to carry out the simpler methods of bacteriological work reference should be made to the standard laboratory text-books, which furnish all necessary details. A good microscope, with a 1/12 oil immersion lens, is, of course, essential. This can now be obtained for about £16 (Beck, Swift, Baker, Watson, etc.), and the other necessary apparatus is readily obtainable of Baird and Tatlock, Hatton Garden, E. C., and other makers.

FOOTNOTES:

[1] _The Contemporary Review_, November, 1897, p. 719.

[2] Some notable exceptions are found in the work of the Bath
and West of England Society, Lord Vernon's model dairy, and
the Essex County Council Bacteriological Teaching Laboratory.

[3] We propose throughout to use the term _bacterium_ (pl.
_bacteria_) in its generic meaning, unless especially stated
to the contrary. It will also be synonymous with the terms
_microbe_, _germ_, and _micro-organism_. The term _bacillus_
will, of course, be restricted to a rod-shaped bacterium.

[4] Migula has recently (1896) suggested that the
Schizomycetes should be subdivided into _Coccaceæ_,
_Bacteriaceæ_, _Spirillaceæ_ (spirilla, spirochæta),
_Chlamydobacteriaceæ_ (Streptothrix, Crenothrix, Cladothrix),
and _Beggiatoa_.

[5] A one-twelfth oil immersion lens is requisite for the
study of the lower bacteria.

[6] A _flagellum_ is a hair-like process arising from the
poles or sides of the bacillus. It must not be confused with
a _filament_, which is a thread-like growth of the bacillus
itself.

[7] A "pure culture" is a growth in an artificial medium
outside the body of one species of micro-organism only.

[8] Some pathogenic germs (suppuration and typhoid) can
withstand freezing for weeks.

[9] G. J. Romanes, _Darwin and After Darwin_, vol. ii., 231.

[10] It will be observed that there is a marked difference
between the effects of dry heat and moist heat. Moist heat is
able to kill organisms much more readily than dry, owing to
its penetrating effect on the capsule of the bacillus. Dry
heat at 140° C. (284° F.), maintained for three hours, is
necessary to kill the resistant spores of _Bacillus anthracis_
and _B. subtilis_, but moist heat at fifty degrees less will
have the same effect. It is from data such as these that in
laboratories and in disinfecting apparatus moist heat is
invariably preferred to dry heat. For with the latter such
high temperatures would be required that they would damage the
articles being disinfected. Koch states the following figures
for general guidance: Dry heat at a temperature of 120° C.
(248° F.) will destroy spores of mould fungi, micrococci,
and bacilli in the absence of their spores; for the spores
of bacilli 140° C. (284° F.), maintained for three hours, is
necessary; moist heat at 100° C. (212° F.) for fifteen minutes
will kill bacilli and their spores.

[11] Water from a house cistern is rarely a fair sample. It
should be taken from the main. If taken from a stream or still
water, the collecting bottle should be held about a foot below
the surface before the stopper is removed.

[12] The _cubic centimetre_ (cc.) is a convenient standard of
fluid measurement constantly recurring in bacteriology. It is
equal to 16-20 drops, and 28 cc. equal one fluid ounce.

[13] The gelatine is reduced to liquid form by heating in
a water-bath. Before inserting the suspected water it is
essential that the gelatine be under 40° C, or thereabouts, in
order not to approach the thermal death-point of any bacteria.

[14] _Micro-organisms in Water_ (1894).

[15] Report on the Micro-organisms of Sewage, Reports to L. C.
C., 1894, No. 216.

[16] Harben Lectures, 1896.

[17] Report on the Metropolitan Water Supply.

[18] The methods adopted for making a quantitative and
qualitative examination of sewage are precisely analogous
to those used in milk research. Dilution with sterilised
water previous to plating out on gelatine in Petri dishes
is essential (1 cc. to 10,000 cc. of sterile water, or some
equally considerable dilution), otherwise the large numbers
of germs would rapidly liquefy and destroy the film. Special
methods must be used for the isolation of special organisms;
phenol-gelatine, Elsner medium, indol reaction, "shake"
cultures, Parietti broth, etc., must often be resorted to for
special bacteria. Spores of bacteria may always be numerically
estimated by adding the suspected water or sewage to gelatine,
and then heating to 80° C. for ten minutes before plating out.
This temperature removes the bacilli, but leaves the spores
untouched.

[19] The bacilli of typhoid can live in crude sewage (Klein),
but only for a very short period. When sewage is diluted
with large quantities of water the case is very different.
_Bacillus coli_ flourishes in sewage.

[20] Annual Report of the Medical Officer of the Local
Government Board, 1897-98, p. 210.

[21] John Tyndall, F.R.S., _Floating Matter of the Air_.

[22] Flügge has lately attempted to demonstrate that an air
current having a velocity of four metres per second can remove
bacteria from surfaces of liquids by detaching drops of the
liquid itself.

[23] Hewlett and Thomson graphically demonstrated the
bactericidal power of the nasal mucous membrane by noting
the early removal of _Bacillus prodigiosus_, which had been
purposely placed on the healthy Schneiderian membrane of the
nose.

[24] _Pathological Society of London, Transactions_, 1897.

[25] _Annali d'Igiene Sperimentale_, vol. v. (1895), fasc. 4.

[26] _Public Health_, vol. x., No. 4, p. 130 (1898).

[27] Flügge, _Grundriss der Hygiene_, 1897.

[28] _Zeitschrift für Hygiene_, vols. xxiv.-xxvi.

[29] _Annales de Micrographie._

[30] E. A. Schäfer, F.R.S., _Text-book on Physiology_, vol.
i., p. 312.

[31] The unorganised ferments are frequently otherwise
classified than as above, not according to the locality, but
according to the function. The chief are these:--_amylolytic_,
those which change starch and glycogen (amyloses) into sugars,
_e. g._, ptyalin, diastase, amylopsin; _proteolytic_, those
which change proteids into proteosis and peptones, _e. g._,
trypsin, pepsin; _inversive_, those which change maltose,
sucrose, and lactose into glucose, _e. g._, invertin;
_coagulative_, those which change soluble proteids into
insoluble, _e. g._, rennet; _steatolytic_, those which split
up fats into fatty acids and glycerine, _e. g._, steapsin.

[32] A chemical change obtained by the action of sulphuric or
some other acid, or by the influence of _diastase_.

[33] _Bacteriology and Infective Diseases_, Appendix.

[34] E. C. Hansen, _Studies in Fermentation_ (Copenhagen), p.
98.

[35] _Proc. Royal Soc. of Edin._, xxxvii., pt. iv., p. 759.

[36] E. A. Schäfer, _Text-book of Physiology_, vol. i., p. 25
(W. D. Halliburton).

[37] "Denitrifying" means reducing _nitrates_.

[38] R. Warington, M.A., F.R.S., _Journ. Roy. Agricultural
Soc. Eng._, series iii., vol. viii., pt. iv., pp. 577 _et seq._

[39] The saltpetre beds of Chili and Peru are an excellent
example of the industrial application of these facts. Nitrates
are there produced from the fæcal evacuations of sea-fowl in
such quantities as to form an article of commerce. A like
form of utilisation of the action of these bacteria was once
practiced on the continent of Europe. Economic application is
also seen in the treatment of sewage referred to elsewhere.

[40] The course of nitrification may be followed by means
of chemical tests. 1. The disappearance of ammonia. 2. The
appearance of nitrite. 3. Its disappearance. 4. Appearance of
nitrate.

[41] Professor Warington, in Report IV. (p. 526) of his
admirable series of papers on the subject, draws attention to
Müntz's criticism that the nitrifying organisms only oxidise
from nitrogenous matter to nitrites, and not from nitrites
to nitrates. Müntz held that the conversion of nitrite into
nitrate is brought about by the joint action of carbonic
acid and oxygen. Professor Warington's experiments, however,
clearly illustrate that the production of nitrates from
nitrites in an ammoniacal solution can be determined by the
character of the bacterial culture with which the solution is
seeded, and that in a solution of potassium nitrite conversion
into nitrate can be determined by the introduction of the
nitric organism. Professor Warington still adheres to the
opinion, in favour of which he has produced so much evidence,
that the formation of nitrates in the soil is due to the
nitric organism which soil always contains.

[42] British Association for the Advancement of Science,
Bristol, 1898, Presidential Address.

[43] British Association for the Advancement of Science,
Bristol, 1898, Presidential Address.

[44] Sir John Lawes and Sir Henry Gilbert (_Times_, December
2, 1898), have pointed out that the addition of nitrates only
would be of no permanent use to the wheat crop. They rely upon
thorough tillage and proper rotation of crops as the means of
improving the nitrogen value of the soil.

[45] Geddes, _Nature_, xxv., 1882.

[46] Sir Henry Gilbert, F.R.S., _The Lawes Agricultural Trust
Lectures_, 1893, p. 129.

[47] _Ibid._, p. 140.

[48] This has been denied recently in the official report
by the chemist of the Experimental Farm to the Minister of
Agriculture at Ottawa (_Report_, 1896, p. 200).

[49] It has already been pointed out that the nitrifying
bacteria, though able to live on organic matter, do not
require such either for existence or for the performance of
their function.

[50] Lehmann and Neumann, p. 305.

[51] The conditions requisite for an outbreak of enteric fever
were, according to Pettenkofer, (_a_) a rapid fall (after a
rise) in the ground water, (_b_) pollution of the soil with
animal impurities, (_c_) a certain earth temperature, and
lastly (_d_) a specific micro-organism in the soil. These
four conditions have not, particularly in England, always
been fulfilled preparatory to an epidemic of typhoid. Yet the
observations necessary for these deductions were a definite
step in advance of mere dampness of soil.

[52] _Supplement to the Report of the Medical Officer of the
Local Government Board_, 1887, p. 7.

[53] _Report of Medical Officer to Local Government Board_,
1895-1896, Appendix.

[54] H. L. Russell, _Dairy Bacteriology_, p. 46.

[55] _Bureau of Animal Industry Reports_, 1895-1896.

[56] _British Medical Journal_, 1895, vol. ii., p. 322.

[57] _British Medical Journal_, 1895, vol. ii., p. 322.

[58] _Journal of Comparative Pathology_, vol. x. (1897), pp.
150-189.

[59] E. W. Hope, M.D., D.Sc., _Report of the Health of
Liverpool during 1897_, p. 40.

[60] S. Rideal and A. G. R. Foulerton conclude, from a series
of experiments, that boric acid (1-2,000) and formaldehyde
(1-50,000) are effective preservatives for milk for a period
of twenty-four hours, and that these quantities have no
appreciable effect upon digestion or the digestibility of
foods preserved by them (_Public Health_, May, 1899, pp.
554-568).

[61] _Report from Wisconsin Agricultural Experiment Station_,
1896.

[62] Jenner Institute of Preventive Medicine (First Series
_Transactions_).

[63] _Centralblatt für Bakteriologie_, etc., II. Abteilung.

[64] _A Manual of Bacteriology, Clinical and Applied_, p. 397.

[65] Hewlett asserts that butter may contain from two to
forty-seven millions of bacteria per gram.

[66] Such pure cultures for such purposes are in the United
States termed "starters," because they start the process of
special ripening. For the sake of convenience the term will be
used here.

[67] The Essex County Council is one of the few public
bodies in England which have undertaken pioneer work in
this department of industry. Under the leadership of Mr.
David Houston, a course of elementary instruction in dairy
bacteriology as applied to modern dairy practice is given in
the County Biological Laboratory at Chelmsford.

[68] _Report of Storr's Agricultural Experiments Station,
State of Connecticut_, 1895.

[69] "Observations on Cheddar Cheese Making," _Reports of Bath
and West and Southern Counties Society_, 1898, pp. 163-171.
Mr. Lloyd's Reports to the West of England Society since
1892 contain various points respecting the application of
bacteriology to cheese-making.

[70] _Journal of Bath and West of England Society_, 1893,
1895, and 1897.

[71] _New York Medical Record_, 1894.

[72] _British Medical Journal_, 1896, ii., p. 760 _et seq._

[73] _Special Report of the Medical Officer to the Local
Government Board on Oyster Culture, etc._, 1896.

[74] Royal Commission on Tuberculosis, _Report_, 1895, pt. i.,
p. 13.

[75] _Ibid._, p. 18.

[76] _British Medical Journal_, 1895, vol. ii., p. 513.

[77] It should be distinctly understood that this table
is merely schematic and provisional. The details of toxin
production and its effect are still open to revision and
amendment.

[78] Sidney Martin, M.D., F.R.S., F.R.C.P., _Croonian Lectures
delivered before the Royal College of Physicians_, June, 1898.

[79] It is impossible here to enter into a detailed
consideration of the various views held with regard to the
formation of antitoxins. It is needless to remark that the
whole matter is one of abstruse technicality and intricacy.
These antitoxic bodies gradually increase in the blood and
tissues, and their action falls into two groups: (_a_)
_antitoxic_, which counteract the effects of the poison
itself; and (_b_) _antimicrobic_, which counteract the effects
of the bacillus itself. "In one and the same animal the blood
may contain a substance or substances which are both antitoxic
and antimicrobic, such, for example, as occurs in the process
of the formation of the diphtheria and tetanus antitoxic
serums" (Sidney Martin).

[80] Types of bodies possessing positive chemiotaxis for
bacteria are the salts of potassium, peptone, glycerine.

[81] Negative chemiotaxis is illustrated in alcohol, and free
acids, and alkalies.

[82] The friend of Addison and Pope, who married Mr.
Edward Wortley Montagu in 1712, and on his appointment to
the ambassadorship of the Porte in 1716 went with him to
Constantinople. They remained abroad for two years, during
which time Lady Wortley Montagu wrote her well-known Letters
to her sister the Countess of Mar, Pope, and others.

[83] Crookshank, _History and Pathology of Vaccination_.

[84] An exhaustive account of vaccine may be found in the
Milroy lectures delivered in 1898 at the Royal College of
Physicians by S. Monckton Copeman, M.D.

[85] Crookshank, _Bacteriology and Infective Diseases_;
Virchow, _The Huxley Lecture_, 1898.

[86] To shorten this period Dr. Cartwright Wood has adopted
a plan by which time may be saved, and 200 cc. injected say
within the first two or three weeks. This is accomplished by
using a "serum toxin" (containing albumoses, but not ferments)
previously to the broth toxin, an ingenious method which we
cannot enter into here.

[87] At the conclusion of the operation the cannula is removed
from the jugular vein, and the wound is closed by the valvular
character of the slit in the skin and vein and the elasticity
of the wall of the vein. No stitching or dressing is required.
Indeed, it is striking to observe in the horse an entire
absence of pain throughout the proceedings.

[88] The term _unit_ is used as a standard measurement. This
means the amount of antitoxin which will just neutralise ten
times the minimum fatal dose of the toxin in a guinea-pig
(250 grams toxin to kill on the fourth day). If 1 cc. of the
antitoxic serum is required for this, one unit is contained in
1 cc.; if 0.01 cc. is sufficient, then 100 units are contained
in the cc. Not less than 1500 units should be administered for
a dose, and repeated every twelve hours. In severe cases two
or three times this amount may be given.

[89] The value of antitoxin treatment in diphtheria is
discussed in the _Brit. Med. Jour._, 1899, pp. 197 and 268, by
E. W. Goodall, M.D.

[90] A detailed study of tuberculosis from its pathological
and bacteriological aspect will be found in _La Tuberculose
et son Bacille_, pt. i., Straus, Professeur à la Faculté de
Médecine de Paris.

[91] For differences of virulence between these conditions
of pulmonary tubercle see Lingard, _Local Government Board
Report_, 1888, p. 462.

[92] _Centralblatt. f. Bact. und Parasit._, vol. vii., p. 9.

[93] _Animal Tuberculosis_, p. 129.

[94] See the _Harben Lectures_, November, 1898, by Sir Richard
Thorne Thorne, Medical Officer to the Local Government Board;
also the _Report of the Royal Commission on Tuberculosis_,
1896-98.

[95] 1. Tuberculosis is a disease mainly affecting the lungs
(_consumption_, _decline_, _phthisis_) of young adults and the
bowels of infants (_tabes mesenterica_). It may affect any
part of the body, and its manifestations are very various. It
also affects animals, particularly cattle, by whom it may be
transmitted to man.

2. _Its direct cause_ is a microscopic vegetable cell, known
as the _Bacillus tuberculosis_, discovered by Koch in 1882.
This fungus requires to be magnified some hundreds of times
before it can even be seen. When it gains entrance to the
weakened body it sets up the disease, which is an _infectious_
disease, though different in degree to the infectiousness of,
say, measles.

3. _Trade influence and occupation_, in some cases,
undoubtedly predispose the individual to tubercle. Cramped
attitudes, exposure to dampness or cold, ill ventilation, and
exposure to inhalation of dust of various kinds, all act in
this way. In support of the evil effect of each of these four
conditions much evidence could he produced.

4. _Overcrowding_ has a definite influence in propagating
tubercular diseases. The agricultural counties without big
towns, like Worcestershire, Herefordshire, Buckinghamshire,
and Rutland, are the counties having the lowest mortality
from tuberculosis; whilst the crowded populations in
Northumberland, South Wales, Lancashire, London, and the
West Riding suffer most. Speaking more particularly, the
overcrowded areas of London, such as St. Giles', Strand,
Holborn, and Central London generally, show very high
tubercular death-rates.

5. _Tuberculosis is not increasing._ During the last thirty
years it has shown, with few exceptions, a steady decline
in all parts of England. "Consumption" is most fatal in
comparatively young people (fifteen to forty-five years),
whilst "tabes" and other forms of tubercle are fatal chiefly
to young children. These forms have not declined so much as
the lung form. The mortality in consumption of males has since
1866 been in excess of that of females. The age of maximum
fatality from consumption is _later_ than in the past, which
is probably due to improved hygiene and treatment.

6. _This decline has been due_, not to any special repressive
measures--for few or none have been carried out--but to a
general and extensive social improvement in the life of the
people, to an increase of knowledge respecting tuberculosis
and hygiene, to an enormous advance in sanitation, and to more
efficient land drainage.

7. _Not all persons are equally liable to consumption_, some
being much more susceptible than others. We have mentioned
the predisposing influence of certain trades. There is also
heredity, which acts, as we have said, in transmitting a
tubercular _tendency_, not commonly the actual virus of
the disease; there is, thirdly, the debilitating effect of
previous illness or chronic alcoholism; there is, fourthly,
the habitual breathing of rebreathed air; and, fifthly, there
are the conditions of the environment, like dampness and
darkness of the dwelling. Such influences as these weaken the
resisting power of the tissues, and thus afford a suitable
nidus for the bacillus conveyed in milk or by the inspiration
of infected dust.

8. _Consumption is curable_ if taken in time. In cases where
the lungs are half gone, and consist of large cavities, it is
obvious that curability is out of the question. But if the
disease can be properly treated in its earliest stages, there
is considerable likelihood of recovery.

9. _The breath is not dangerous_, as far as we know, but there
is danger from discharges of any kind from any infected part,
whether lungs or bowels; for such discharges, when dry, may
readily pollute the air, and either the bacilli or spores be
inhaled into the lungs.

10. _The chief channels of personal infection or the spread
of the disease amongst a community_ are two: (_a_) dried
tubercular sputum (or other tubercular discharges); (_b_)
infected milk or meat. So long as the former remains wet or
moist, infection cannot take place. It is, of course, better
to destroy it completely. As for milk and meat, boiling the
former and thoroughly cooking the latter will remove all
danger.

11. _The expectoration is infective._ This is one of the
commonest modes of infection, and to it is held to be due
the large amount of respiratory tuberculosis (consumption,
phthisis). The expectoration from the lungs must contain, from
the nature of the case, a very large number of bacilli. As
a matter of fact, a single consumptive individual can cough
up in a day millions of tubercle bacilli. When expectoration
becomes dry, the least current of air will disseminate the
infective dust, which can by that means be readily reinspired.
Expectoration on pavements and floors, as well as on
handkerchiefs, may thus become, on drying, a source of great
danger to others. The discharges from the bowels of infants
suffering from the disease also contain the infective material.

12. _Milk_, though a much more likely channel for conveyance
of tubercle than meat, is only or chiefly virulent when the
udder is the seat of tuberculous lesions. The consumption of
such milk is only dangerous when it contains a great number of
bacilli and is ingested in considerable quantity. Practically
the danger from using raw milk exists only for those persons
who use it as their sole or principal food, _e. g._, young
children. All danger is avoided by boiling or pasteurising the
milk.

At the same time there is an increasing amount of evidence
forthcoming at the present time which goes to prove that milk
is not infrequently tainted with tubercle (see p. 195). The
tuberculin test should be applied to all milch cows, and the
infected ones isolated from the herd. Milk supplies should be
more strictly inspected even than cowsheds.

13. There are several methods by which _meat infection can
be prevented_. In the first place, herds should be kept
healthy, and tubercular animals isolated. Cowsheds and byres
should be under sanitary supervision, especially as regards
overcrowding, dampness, lack of light, and uncleanliness.
Public slaughter-houses under a sanitary authority would
undoubtedly be most advantageous. Meat inspection should also
be more strictly attended to; efficient cooking, and avoidance
of "roll" meat which has not been thoroughly cooked in the
middle.

14. _Consumptive patients may diminish their disease._ Dr.
Arthur Ransome[95a] has laid down five axioms of hygiene for
phthisical patients which, if followed, would materially
improve the condition of such persons. At Davos, St. Moritz,
Nordrach and other places where they have been practised, the
beneficial change has been in many cases extraordinary:

(1) Abundance of light, nutritious, easily digested food,
which must comprise a large allowance of fat; small meals, but
frequent;

(2) An almost entirely open-air life, with as much sunshine as
can be obtained;

(3) Suitable clothing, mostly wool;

(4) Cleanliness and bracing cold-water treatment;

(5) Mild but regular exercise.

15. _Consumptive patients may also assist in preventing the
spread of the disease._ In the first place, they should
follow the hygienic directions just mentioned, because such
conditions fulfilled will materially lessen the contagiousness
of such patients; next, the expectoration must never be
allowed to get dry. A spitting-cup containing a little
disinfectant solution (one teaspoonful of strong carbolic acid
to two tablespoonfuls of water) should always be used, or the
expectoration received into paper handkerchiefs which can be
burnt. Spoons, forks, cups, and all such articles should be
thoroughly cleaned before being used by other persons. The
patient should not sleep in company with another, but occupy,
if possible, a separate bedroom.

Isolation hospitals for consumptives, as for patients
suffering from diphtheria, are now being established.

16. _House influence_ has some effect, both directly and
indirectly, upon tubercular diseases. Damp soils, darkness,
and small cubic space in the dwelling-house exert a very
prejudicial effect upon tubercular patients. Sir Richard
Thorne Thorne[95b] has described the favourable house for such
persons as one built upon a soil which is dry naturally or
freed by artificial means from the injurious influences of
dampness and of the oscillations of the underlying subsoil.
The house itself should be so constructed as to be protected
against dampness of site, foundations, and walls. Upon at
least two opposite sides of the dwelling-house there should be
enough open space to secure ample movement of air about it,
and free exposure to sunlight. Lastly, it should be possible
to have free movement of air by day and night through all
habitable rooms of the house. It is clear that many inhabited
houses could not stand to these tests; but effort should be
made to approach as near to such a standard as possible.

17. _Sunlight and fresh air_ are the greatest enemies to
infection.

18. _Disinfection is necessary after death from phthisis_,
and should be as complete as after any other infective
disease. Compulsory notification of fatal cases and compulsory
disinfection have been officially ordered by the Prussian
Government. In this country also absolute disinfection should
always be insisted upon after phthisis. Walls, floors,
carpets, curtains, etc., should be strictly sterilised.
Professor Delepine recommends spraying with 1-100 solution of
chloride of lime.

[95a] Arthur Ransome, M.D., F.R.S., _Treatment of Phthisis_.

[95b] _Practitioner_, vol. xlvi.

[96] _Journal of State Medicine_, vol. iv. (1896), p. 169.

[97] For a fuller statement see _Trans. Jenner Institute_
(First Series), pp. 7-32.

[98] See _Trans. Jenner Institute_ (First Series), A. G. R.
Foulerton, pp. 40-81.

[99] Dated 1890-91. The Commissioners were the late Beaven
Rake, M.D., G. A. Buckmaster, M.D., the late Professor
Kanthack, of Cambridge, the late Surgeon-Major Arthur Barclay,
and Surgeon-Major S. J. Thomson.

[100] _Bacteriology and Infective Diseases_ (1896), p. 144.
Professor Crookshank's Reports to the Agricultural Department
of the Privy Council constitute the most complete account of
this disease hitherto published.

[101] _Zeitschr. f. Hyg. und Inf. Krank._, xxv.

[102] _Journal of State Medicine_, December, 1897, p. 561.

[103] _Bacteriology and Infective Diseases_, p. 35.

[104] _British Medical Journal_, 1895 (February), p. 353.

[105] _British Medical Journal_, 1896 (August), p. 439.

[106] _Journal of State Medicine_, 1898 (November), p. 541.

[107] The measurement of cubic space is of course made by
multiplying together in feet the length, breadth, and height
of a room.

[108] _British Medical Journal_, 1898 (April), p. 1013.

INDEX

Abscess formation, 296-301

Acetous fermentation, 115, 127

Actinomycosis, 316

Aërobic organisms, 26

Agar, 21

Air, bacteriology of, 96-110

-- examination of, 96-99

-- of sewers, 105

-- expired, 102

-- bacteria and gravity, 106

-- standard of bacteria in, 108

-- pathogenic bacteria in, 109

-- passages, bacteria in, 103

Alcohol, formation of, 115

Alcoholic fermentation, 115, 117

Alexines, 249, 268

Alformant lamp for disinfection, 334

Algæ in water, 53

Ammoniacal fermentation, 115

Amylolytic ferments, 115

Anaërobic organisms, 132

-- methods of culture, 139-142

-- in hydrogen, 139, 140

-- in glucose-agar, 142

-- in Fränkel's tube, 140

-- in Buchner's tube, 141

Aniline dyes, 44

Antagonism of organisms, 33

Anthrax, 19, 26, 30, 34, 245

-- pathology of, 301

-- spores of, 302

-- bacillus of, 302

Antiseptics, 323, 332

-- definition of, 322

-- some of the chief, 332

Antitoxins, 245-250

-- preparation of, 259

-- use of, 263

-- unit of, 263

Appendix, 337

Arthrospores, 17

Artificial purification of water, 73

Ascospores, 120

Asiatic cholera, 65

Association of organisms, 31

Attenuation of virulence, 36

Bacillus, definition of, 11

-- aceti, 34, 129

-- acidi lactici, 131, 185, 190

-- amylobacter, 132

-- anthracis, 26, 31, 34, 110, 301-305

-- aquatilis, 53

-- butyricus, 133

-- coli communis, 32, 56, 58-62, 64, 67, 86, 88, 108, 151, 194, 237, 299,
315

-- cyanogenus, 193

-- diphtheriæ, 201, 212, 244, 289-296

-- enteriditis sporogenes, 60, 86, 87, 316

-- erythrosporus, 53

-- fluorescens liquefaciens, 43, 53, 64, 86

-- fluorescens non-liquefaciens, 53, 15

-- of cholera, 65-69

-- of diarrhœa, 203, 204

-- of influenza, 315

-- lactis erythrogenes, 193

-- lactis pituitosi, 193

-- lactis viscosus, 193

-- liquefaciens, 53, 151

-- of leprosy, 308-313

-- of glanders (mallei), 299, 319

-- mesentericus, 86, 151

-- mycoides, 151

-- of malignant œdema, 19, 172

-- No. 41, 219

-- pasteurianum, 130

-- of scarlet fever, 202

-- of symptomatic anthrax, 19, 171, 172

-- of plague, 306-308

Bacillus prodigiosus, 34, 151, 193, 238

-- pyocyaneus, 7, 34, 64, 110, 299

-- pyogenes fœtidus, 34

-- radicicola, 164

-- saponacei, 193

-- subtilis, 31, 86, 108

-- synxanthus, 194

-- of tetanus, 19, 168-171

-- termo, 53

-- of tubercle, 110, 212, 225, 274-291

-- typhosus, 41, 50, 55-62, 212

-- ubiquitous, 53

-- of yellow fever, 316

Bacteria, action of, 26

-- in sewage, 84

-- and wheat supply, 161

-- and fixation of nitrogen, 160-166

-- in cheese-making, 220-227

-- in the dairy, 215-227

-- products of, 240, 241

-- and disease, 264-321

-- the higher, 11, 33

-- in soil, 137-177

Bacterial action, 26

-- treatment of sewage, 90

Bacteroids, 166

Beer diseases, 134

Berkefeld filter, 52

Biogenesis, 3

Biology of bacteria, 1-36

Bitter fermentation, 191

Blood serum, 22

Blue milk, 193

Boracic acid, 205, 331

Bread, bacteria in, 238

Broth, 21

Brownian movement, 14

Bubonic plague, 306-308

Buchner's tube, 141

Butter, bacteria in, 213, 214

-- examination of, 214

-- bacterial flavouring of, 215

Butyric fermentation, 115, 132, 191

Carbol-fuchsin, 44

Carbol-gelatine, 62

Carbolic acid as a germicide, 332

Caries, dental, 104

Chamber, moist, 41

Channels of infection in disease, 269

-- in tubercle, 289

Cheese, bacteria in, 220

Chemical products of bacteria, 241

Chemical substances as disinfectants, 329

-- and bacteriological examination of water compared, 51

-- tests for nitrification, 158

Chemiotaxis, 15, 248

Chicken cholera, 320

Chinosol as a disinfectant, 336

Chloride of lime as a germicide, 331

Cholera, 65-68

-- diagnosis of, 68

-- and filtration, 75

-- and milk, 200

Chromogenic bacteria, 193, 241

Cladothrix, 8, 33

Clark's process, 73

Classification, 7

Coccus, definition of, 8

Colon bacillus, _see_ B. coli communis

Comma bacillus, 66

Commensalism, 162

Composition of bacteria, 12-14

Conditions affecting bacteria in water, 70

-- in milk, 186, 187

Contagion, 270

Corrosive sublimate as disinfectant, 331

Counter (Wolfhügel), 49

Cover-glass preparations, 44

Cream, bacteria in, 213

Crenothrix polyspora, 53

Creosol as a germicide, 332

Cultivation beds, 92

Culture media, 20

-- anaërobic, 139

-- hanging drop, 44

-- plate, 40-43

-- pure, 20, 46

-- shake, 62

Decomposition bacteria, 149

Denitrifying bacteria, 143, 149

Dental caries, 104

Deodorants, 323

Desiccation, 26

Diagnosis, 339

Diarrhœa of infants, 175, 316

Diphtheria, 243-245, 289-296

-- bacillus of, 289

-- toxins of, 244, 293

-- and milk supply, 201

-- and school influence, 294, 295

-- pseudo-bacillus of, 296

Diplococcus, definition of, 8

Diplococcus of gonorrhœa, 300

-- in pneumonia, 313

Directions for estimating disinfectants, etc., 324

Disease, production of, 264

Diseases of beer, 134

-- of plants, 35

-- of animals, 316-320

-- conveyed by water, 81

-- and soil, 173-177

Disinfectants, 322, 331

Disinfection, 322-336

-- of a room, 335

-- of walls, 335

-- of bedding, 335

-- of garments, 335

-- of excreta, 335

-- of wounds, 336

-- of hands, 336

Domestic purification of water, 79

Dunham's solution, 69

Dysentery, 319

Earth temperatures and disease, 175

Economic bacteria, 145

Egg cultures, 340

Elsner's medium, 62

Endospores, 17

Enteric fever, _see_ Typhoid

Enzymes, 114

Equifex disinfector, 328

-- sprayer, 334

Erysipelas, 299

Examination, bacteriological--

-- air, 96-99

-- cholera, 68

-- diphtheria, 290, 340

-- leprosy, 309

-- meat, 234

-- milk, 227

-- sewage, 80

-- soil, 138

-- tetanus, 170

-- tubercle, 276, 339

-- water, 43-48

-- yeasts, 119, _et seq._

Extracellular poisons, 244, 273

Fermentation, 111-136

-- acetous, 115, 127

-- alcoholic, 115, 117

-- ammoniacal, 115, _see_ under Soil

-- butyric, 115, 132, 191

-- lactic acid, 115, 130, 190

Ferments, organised, 114, 115

Ferments, unorganised, 114, 115

-- chromogenic, 193

-- curdling, 191

-- bitter, 191

-- slimy, 192

-- soapy, 193

Films, 123

Filter, domestic, 79

Filter-beds, 74

Filtration, milk, 206

-- method of air examination, 99

-- sand, 77-79

Fission, 16

Fixing specimens, 45

Flagella, 15

-- staining, 63

Food, bacteria in, 179, 180

Foot-and-mouth disease, 320

Formaldehyde and formalin, 205, 206, 333

Forms of bacteria, 8

Fränkel's tube, 140

-- pneumococcus, 314

Friedländer's pneumo-bacillus, 315

Gas, production of, 62, 241

Gathering-ground, 38

Gelatine, 21

-- carbol, 62

-- liquefaction of, 44

Gemmation, 119

Gentian-violet, aniline, 44

Germicidal temperatures, 30, 207

Germicides, 322, 331

Glanders, 319

Gonorrhœa, 300

Gram's method, 44, 338

Gravity, influence on bacteria, 106

Gypsum block, 121

Hæmatozoa, 320

Hanging drop cultivations, 44

Hansen's method of dilution, 123

Heat as steriliser, 30, 326

Heredity, 268, 269

Hesse's method of air examination, 98

Higher bacteria, 11

High yeasts, 125

Hot air steriliser, 31

Hydrogen cultivation, 139

Hydrophobia, treatment of, 253

Ice-cream, bacteria in, 236-238

-- examination of, 236

Immunity, 240-263

-- acquired, 247, 250

-- active, 250

-- artificial, 250

-- natural, 250

-- passive, 250

Incubation period, 271

Incubators, 22

Indol, formation of, 61

-- testing for, 61

Industries and bacteria, 135

Influenza, 315

Intracellular poisons, 34

Inversive ferments, 115

Involution forms, 12, 66

Kipp's apparatus for producing hydrogen, 27, 139

Klebs-Löffler bacillus, 289

Koch's plate method, 40

-- postulates, 266

-- comma bacillus, 66

-- bacillus of tubercle, 276

Lactic acid fermentation, 115, 130, 185, 190, 221, 226

Lactose, 190

Leguminosæ, fixation of nitrogen by, 163

Leprosy, 308-313

Leptothrix, 8, 33

Leuconostoc, 17

Light, influence upon bacteria, 24-26, 70

Liquefaction of gelatine, 44, 241

Low yeasts, 125

Lymph, glycerinated calf, 252

Lyon's, Washington, disinfector, 328

Maceration industries, 135

Malaria, 177, 320

Malignant œdema, 19, 172

Mallein, 319

Mastitis, 184

Measles, 321

Meat, 234

Media, culture, 20

Merismopedia, 11

Method of examination, 43-47

Metropolitan water supply, 72

Miasmatic diseases, 176

Micrococcus, definition of, 8

-- agilis, 16

-- aquatilis, 53

-- casei amari, 226

Micrococcus Freudenreichii, 192

-- gonorrhϾ, 299

-- tetragonus, 299

-- viscosus, 192

Milk, bacteriology of, 178-213

-- absorptivity of, 180

-- sources of pollution, 181-184

-- number of bacteria in, 185

-- influence of temperature upon, 186

-- influence of time of standing, 187

-- fermentation bacteria in, 189

-- constitution of, 189-195

-- disease-producing power of, 195

-- and tuberculosis, 197-199, 228, 290

-- and typhoid, 199

-- and cholera, 200

-- and diphtheria, 201

-- and scarlet fever, 202

-- and thrush, 203

-- methods of preservation of, 205

-- and added antiseptics, 205, 206

-- filtration of, 206

-- sterilisation of, 207

-- pasteurisation of, 208-213

-- products, bacteria in, 213-227

-- examination of, 227

-- and economic bacteria, 215-220

-- sterile, 181

-- kinds of bacteria in, 188

-- chromogenic, 193

-- cooling processes, 207, 209

Moist chamber, 41

Moisture necessary for bacteria, 23

Motility, 14

Moulds, 116

Mycoderma aceti, 127

Nasal passages, bacteria in, 103

Natural purification of water, 69

Needles, platinum, 22, 24

Nitrates, 147, 154

Nitric organism, 157, 158

Nitrification, 76, 143-159

-- chemistry of, 144-148

-- stages in, 145

-- bacteria of, 152

Nitrifying organisms, cultivation of, 156

Nitrogen, fixation of, 144, 160-168

Nitrous organism, 154, 158

Nodules on roots, bacteria in, 163

Oidium albicans, 203

Oxygen necessary for bacteria, 26

Oysters and bacteria, 229-234

Paraform for disinfection, 334

Parasitism, 27, 162

Parietti's method, 62

Pasteurisation of milk, 208-213

Pasteur's treatment of rabies, 253-258

Perlsucht, 283

Petri dishes, 50

Phagocytosis, 247

Phosphorescence, 26, 241

Pigment, formation of, 241

Place of bacteria in nature, 5

Plague, 306-308

Plant diseases, 35

Plate cultures, 40-46

Platinum needles, 22, 24

Pleomorphism, 12

Pneumo-bacillus, 315

Pneumococcus, 313

Pneumonia, 313

Polymorphism, 12

Postulates, Koch's, 266

Potato medium, 22

Pouchet's aëroscope, 96

Proteolytic ferments, 115

Proteus family, 86, 180, 297

-- vulgaris, 60, 86, 151, 194

-- zenkeri, 60

Pseudo-diphtheria bacillus, 296

Ptomaines, 179

Pure culture, 20, 46

Purification of water--

-- natural, 69

-- artificial, 73

Pus, 296

Putrefaction, 143-149

Pyocyanin, 299

Pyoxanthose, 299

Quantitative standard for water bacteria, 48, 49

-- air bacteria, 107

-- milk bacteria, 188

-- soil bacteria, 137

Quarter evil, 19, 171

Rabies, treatment of, 253

-- forms of, 253

-- pathology of, 254

-- results of treatment, 256

Reck's disinfector, 328

Reproduction of bacteria, methods of, 16

Retting, 135

Rinderpest, 320

Saccharomycetes, biology of, 119-121

-- methods of examination, 122

-- anomalous, 122

-- apiculatus, 127

-- aquifolii, 127

-- cerevisiæ, 117, 124, 126

-- conglomeratus, 126

-- ellipsoideus I., 126

-- ellipsoideus II., 126, 134

-- exiguus, 127

-- Hansenii, 127

-- illicis, 127

-- Ludwigii, 122

-- mycoderma, 127

-- pastorianus I., 127, 134

-- pastorianus II., 127

-- pastorianus III., 127, 134

-- pyriformis, 127

Salicylic acid as antiseptic, 205, 206

Saprophytes, 27, 166

Sarcina, 10

Scarlet fever, 202, 321

Sedgwick's method of air analysis, 99

Sedimentation, 71, 73

Septic processes, 296

-- tank, 90

Sewage, organisms in, 84

-- bacterial treatment of, 89

Sewer air, 87

-- and toxicity of bacteria, 105

Shake culture, 62

Shell-fish and bacteria, 229, 234

Small-pox, 251, 321

Soil, bacteriology of, 137

-- examination of, 138

-- kinds of bacteria in, 142-145

-- and its relation to disease, 173, 176, 177

Species of bacteria, 29

Spirillum, definition of, 11

-- of cholera, 66

Spontaneous generation, 2

Spores, kinds of, 17-19

-- resistance of, 19, 278

-- staining of, 19

-- of yeasts, 122

Staining methods, 45

Staphylococcus, 10, 296

-- cereus albus, 297

-- pyogenes aureus, 88, 108, 297

Steam as a disinfector, 326

-- disinfectors, 327-329

-- steriliser, 326

-- saturated, 327

-- superheated, 327

Steam current, 327

Sterilisation, 29-31

-- methods of, 30, 31

Streptococcus, 9, 297

-- pyogenes, 299

-- Hollandicus, 192

Streptothrix, 317

Structure of bacteria, 8

Sulphurous acid as a germicide, 332

Suppuration, 296-301

Swine fever, 320

Symbiosis, 162

Symptomatic anthrax, 171

Table of economic bacteria in soil, 145

Temperature, influence of, on bacteria, 23

Tetanus, 19, 168, 245

-- toxin of, 168

Thresh's disinfector, 328

Thrush, 203

Tissues, effect of, on bacteria, 267

Tobacco-curing, 136

Toxins, 28, 241-247, 272

Tuberculin, 281

Tuberculosis, 274-292

-- pathology of, 274

-- varieties of, 275

-- history of, 276

-- conveyed by the air, 104

-- and the milk supply, 196-198, 290

-- giant cells in, 275

-- bacillus of, 276

-- cultivation of bacillus of, 277

-- spores of, 277

-- relation of bacillus to disease, 279

-- toxins of, 281

-- of animals, 283

-- prevention of, 286-292

-- disinfection in cases of, 292

-- decline of, 288

-- and overcrowding, 288

-- channels of infection in, 289

-- expectoration in, 290

Tuberculosis and house influence, 291

-- and glanders, 319

Typhoid fever, 56

-- bacillus of, 55-58

-- micro-pathology, 57

-- bacillus compared with B. coli, 58

-- bacillus in sewage, 59

-- bacillus in drinking water, 60

-- tests for bacillus of, 61-64

-- and soil, 173, 176

-- conveyed by the air, 105

-- and milk supply, 199

Tyrotoxicon, 205, 237

Unit of antitoxin, 263

Urea, 148

Vaccination, 251-253

Vaccines, plague, 257, 259

-- cholera, 257

-- small-pox, 251

Vaccinia, 251

Variolation, 250, 251

Virulence increased, 32

-- diminished, 36

Water, bacteria in, 37-84

-- number of bacteria in, 38

-- examination of, 39-52

-- disease organisms found in, 55

-- natural purification of, 69

-- artificial purification of, 73

-- filtration of, 74

-- domestic purification of, 79

-- pollution of, 82

Wheat supply and bacteria, 161

Widal reaction, 63, 340

Wooden tongue, 318

Wool-sorters' disease, 305

Yeasts, 116

Yellow fever, 316

Ziehl-Neelsen stain, 44, 340

The Science Series

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