Chapter IX: Part 9

There are many exceptions to the above-mentioned failures to produce infections in animals. Cantani obtained very constant positive results by subdural injections. He first clearly showed that killed cultures were markedly toxic and that virulence could be raised very definitely by animal passage. By injecting brain emulsion with a culture he obtained a subcutaneous abscess in a rabbit which after eight days still contained the living organism. Nastjukoff found that animals with a lowered resistance, or definitely ill from, for example, an artificial tuberculosis, became infected while others did not. Jacobson showed that B. influenzæ injected with streptococci caused a definite mixed infection, and that after six passages the influenza bacillus alone could produce a fatal infection. Saathoff (1907) confirmed Jacobson’s findings and found pneumococci equally effective. Davis (1915) also confirmed the principle established by Jacobson of the symbiotic relation of other bacteria to infection with B. influenzæ. He used a culture of a non-virulent staphylococcus pyogenes aureus, and was able to produce death invariably in guinea pigs after intraperitoneal injection. From the heart’s blood, as a rule, only the hemophilic bacillus was recovered. He also found animal passage increased the virulence, and further that M. catarrhalis and an avirulent streptococcus had the same effect as the staphylococcus. Slatineanu (1901) found that he could infect animals with B. influenzæ if the cultures were injected along with weak solutions of lactic acid, and that after animal passage by this method the bacillus became more virulent and would eventually kill by itself. It must not be forgotten in this connection that strains of B. influenzæ from meningitis cases are frequently definitely pathogenic for animals. The importance of considering these various factors in a discussion of infection by this organism is, of course, very evident. Ecker found his strains pathogenic for mice after subcutaneous injection, and the bacilli were readily obtained from the heart’s blood. Spooner and his co-workers from their results of more than a hundred intraperitoneal injections concluded that the organism is not pathogenic for mice.

In all animal experiments it is of the greatest importance that the bacteria be known which may interfere in the experiments through spontaneous infection (often liable to be induced by the injection) from the animal’s own flora, as well as the greater susceptibility of previously diseased animals (Nastjukoff). It would appear from the results of Bruschettini and Cornil and Chantemesse in the early days of the influenza bacillus, and those of Lamb and Brannin in their recent study, that these authors did not seriously consider the spontaneous infection of guinea pigs and rabbits with B. bronchisepticus or the bacillus of rabbit septicæmia, both morphologically, very similar to B. influenzæ. Rosenow in his experiments with streptococci from cases of influenza has also apparently failed to realize the importance of the lung lesions produced by the B. bronchisepticus in guinea pigs as reported by Theobald Smith, myself and many others.

Parker has found a filterable poison from the influenza bacillus which developed rapidly (6 to 8 hours) in a special heated blood broth medium, deteriorated rapidly even in the cold, and killed rabbits in quantities of 2 c.c. in from 1 to 3 hours. Rabbits could further be immunized against this poison, and their sera protected other rabbits against fatal doses. This is the first time that a true powerful toxine has been obtained. Couret and Herbert obtained toxine from B. influenzæ in Avery’s oleate broth. Huntoon and Ross also clearly demonstrated toxine production by this organism so that it would appear, with this confirmation, that the B. influenzæ can be definitely classed among the toxine producers. Toxemia being the most striking clinical characteristic of influenza, we have in these findings very strong evidence of the etiological importance of this hemophilic bacillus to the disease. A very interesting observation was made by Latapie that the serum of a goat immunized against influenza bacillus is toxic if it is used shortly after the injection of the microbes, but that this toxicity is absent three weeks after the last injection. It would appear to me that the evidence of a filterable virus from the secretions of the respiratory tract does not eliminate the very probable toxine from such materials. The production of toxine by this organism probably depends, as is the case with very many of our toxine formers, on the most favorable combinations of conditions. That it is not readily formed in artificial cultures, or that it is very unstable if formed, is evidenced by the frequent failures of a great many workers. It has been suggested that different symbiotic conditions in the respiratory tract determine the amount of toxine produced. Huntoon found a high toxine production in mixed cultures with streptococci. This, however, does not appear to be necessary, as there is ample evidence of severe toxemia from pure infections with B. influenzæ in various parts, such as the accessory sinuses of the head, the meninges, the lungs and other parts of the respiratory tract.

It is not fundamentally necessary that a toxine producing organism be present in overwhelming numbers before it can be accepted as the cause of the toxemia. Nor, on the other hand, must we have toxemia every time the organism is found. The prevalent idea among bacteriologists would appear to be the reverse of what I have just stated. It would, indeed, be extremely difficult to make bacteriological diagnoses of a great many of our diseases, where the etiological factor is well established, if these conditions were required. We do not do so, for example, in diphtheria, examinations of stools for typhoid, nor in infections with the tetanus bacillus. We recognize carrier cases of meningococcus, B. typhosus, hemolytic streptococci and many others, without detracting seriously from their importance in definite types of infection. Formerly the specificity of the different bacteria for definite disease processes was very rigid, but today we interpret more broadly the finding of gonococcus in endocarditis, the meningococcus in bacteremia, B. typhosus in osteomyelitis, streptococci and pneumococci in all manner of infections and many other bacteriological results. True it is that the various bacteria show predilections for attacking certain tissues, but the varying susceptibilities bring about the greatest variations in the manifestations of these infections.

The B. influenzæ is not confined to the causation of severe pandemic or epidemic influenza, but includes in its field purulent bronchitis, meningitis, sinusitis, conjunctivitis and many other pathological processes. It further should be recognized as a relatively frequent cause of complications in measles and other diseases.

_Infections of the Respiratory Tract_

The disease influenza is primarily an infection of the respiratory tract. It varies from one of the most acute and fatal diseases we know of through all grades of severity—from chronic infections lasting over years to the familiar three or five day fever. This graduation is to be found more or less marked in all our bacterial infections, but would seem to be not generally recognized or appreciated as occurring in infections with the influenza bacillus. That Pfeiffer was dealing with one phase of the disease when the influenza bacillus was discovered does not invalidate the results of numerous workers which have been added since then.

Probably the greatest confusion in attempts to get a clear picture of this protean disease has been and is a non-recognition of influenza as a frequent complication of other diseases, such as measles (Jochmann, Susswein, Tedesko and very many others). The second cause for this confusion has been the misinterpretation of the facts demonstrating the rather frequent occurrence of carriers. During an epidemic the vast majority of patients show the disease as an upper respiratory infection of varying degrees of intensity, but which usually subsides after periods of from three to five days of fever. Along with this we have other graded manifestations of further involvement of the tract with laryngitis, bronchitis, bronchiolitis and all degrees of broncho-pneumonia. To prevent the severe lung involvement prompt treatment must be carried out, under which rest in bed is by long odds the most important. This will be discussed in another paper of this series, and was particularly well demonstrated in the results at the Naval Hospital as verbally reported to me by D. G. Richey. The interesting point is that the infection can be controlled, but this does not indicate the etiological factor as different from that acting in the more severe cases.

The epidemiological evidence would seem to show very clearly that the incubation period is approximately two days, and that a period of six weeks is the usual limit for the severe wave of the epidemic in different localities. In my opinion, during this period every exposed individual in a community has received the influenza bacillus in the respiratory tract, and that all the susceptible individuals are attacked and show more or less evidence of the infection. As a consequence of this general distribution we have great numbers of individuals carrying the organism, and the aftermath is to be noted in other and later manifestations of the same infection.

Sporadic cases of influenza appear during inter-epidemic periods and more or less healthy carriers are frequent. Scheller’s study in Königsberg showed, if we can rely on his figures, that the carriers were very numerous during an epidemic year (winter 1906-1907), being 24 to 33 per cent.; that as the epidemic became less widespread (winter 1907-1908) it fell to 10 to 13 per cent.; as it was disappearing (summer 1908) he found only 1.5 to 3.3 per cent.; while when the epidemic was completely over (winter 1908-1909) there were no carriers of B. influenzæ found. These results are taken from studies of sputa and throat smears of 138, 218, 155 and 185 cases, respectively, for the periods mentioned. The monumental work of Tedesko, who reported the results of 1,479 cultures, covering 11 years (1896-1906), would indicate that B. influenzæ is continually present in the population. However, in carefully analyzing his results, it is very clear that in the great majority of his cases it was of definite etiological significance. Lobular pneumonia, acute, purulent and chronic bronchitis, and most frequently clinical influenza, are the prominent diagnoses in all his tables. He was able to grow B. influenzæ repeatedly from individual patients for many months.

Lord in similar studies (1902, 1905, 1908) brought out somewhat similar facts. He laid particular stress on the cases of chronic bronchitis with numerous B. influenzæ in the sputum and a probable confusion of these with pulmonary tuberculosis. He was able to follow a number of his patients for several years. B. influenzæ was grown in culture from the sputum of one of these in 1902; in November, 1903; in February, 1904, and in February, 1905. In other cases the organism was shown to be present by culture practically continuously for months and even years. Lord, with Scott and Nye, in a recently published article (1919) reviewed his former results and showed a relatively high incidence of B. influenzæ in the respiratory tract of apparently healthy people. Davis studied 534 cases, further indicating the prevalence of this organism in the community.

The B. influenzæ has been recovered from the respiratory tract during the clinically pure influenza, from the sputum and lung in influenzal pneumonia, and from the purulent sputum in all grades of bronchitis. These should all be looked upon as true infections by the influenza bacillus, the varying manifestations merely differing with the resistance of the individual. In the epidemic in the fall of 1918 pneumonia was the outstanding feature. Preceding this in the English publications we have reports of outbreaks of purulent bronchitis. Macdonald and his co-workers, finding the B. influenzæ frequently present, considered the condition as one indication of a virulent infection by this organism. Hammond, Rolland and Shore reported similar cases, and Abrahams and his co-workers looked upon the cases of purulent bronchitis as occupying a position, without any definite line of demarcation, between those with definite broncho-pneumonia on the one side and those with simple bronchial catarrh on the other. H. E. Robertson emphasized the serious nature of influenzal purulent bronchitis and the almost epidemic character and rather high mortality of the outbreak in the winter and spring of 1917-1918. There were also numerous mild outbreaks of influenza before the overwhelming culmination of the last three months of 1918, as reported by Orticoni and many others and noted by Johnston in this series of papers. Greenwood in an epidemiological study emphasized the point, previously made evident by Parsons for the pandemic of 1889-1892, that the mass attack is preceded by numbers of individual cases. In this country it was noted during the winter of 1917-1918 and the following spring that the B. influenzæ was rather frequently found in the respiratory infection in our army camps (Soper, Cole and MacCallum and others).

It is well recognized that when the actual epidemic struck there were comparatively few bacteriologists familiar with the B. influenzæ. The real difficulties of isolation, the more favorable media, the facts of symbiosis, the importance of carriers, the varying manifestations of the infection and many of the other vitally important points, although more or less fully reported in the literature, were nevertheless practically unknown. It was my own experience, and that of many others. This must be seriously considered in analyzing many of the reports on bacteriological findings throughout the period of the severe wave and even after.

_Results of Others During the Recent Pandemic_

It will be impossible to review the numerous reports on the recent epidemic that have appeared. Many of these can be discounted, as far as the finding of B. influenzæ is concerned, for the reasons mentioned above. The often quoted report of Little, Garofalo and Williams, who did not even use a hemoglobin medium, will serve as an example. Little attention should be given to others where the large numbers of cases precluded the requisite time and media necessary for such a difficult problem. Friedlander and his co-workers in their report from Camp Sherman made no mention of the number of sputa, throat swabs or autopsies which they examined bacteriologically. The incidence of influenza showed a total of 10,979 cases, 2,001 of pulmonary œdema or pneumonia and 842 deaths. They recorded one culture from the sputum with pneumococcus predominating which gave two colonies of B. influenzæ, and this bacillus was grown from the lung exudate at one autopsy. Their conclusions that “B. influenzæ (Pfeiffer) has not been demonstrated as the causative organism” is certainly true from their results, but that “the frequency of its detection has not exceeded the frequency of its existence under normal conditions” can hardly be considered as established, if we accept the many results mentioned above as indicating its presence during inter-epidemic times, unless they mean by normal conditions practically complete freedom from this organism.

The prevalence of B. influenzæ in various sections of this country may be indicated by the following reports chosen from many available ones. Keegan, from the First Naval District Hospital, found B. influenzæ 19 times from 23 in cultures grown from the lungs. In 6 cases these cultures were pure. Medalia reported from Camp McArthur the following. Out of 2,279 sputa of influenza suspects, 76.8 per cent. showed “B. influenzæ” in smears, and 445 sputa from cases of broncho-pneumonia showed it in 54 per cent. It was found in culture in only 10.6 per cent. of these last cases. He considered sputum smears of practical diagnostic help. He further grew B. influenzæ twice from the blood during life, once with a pneumococcus and once alone. Necropsy cultures gave B. influenzæ in 2 of 3 cultures from the brain, 19 of 34 from the heart, 19 of 36 from the spleen, 54 of 65 from both lungs, 50 of 62 from the right pleura and 47 of 62 from the left pleura. The percentage of positive results ranged from 53 in the spleen to 83 in the lungs. Nuzum and his associates only found B. influenzæ in 4 of 100 cases from the bronchial secretions, but it is interesting to note that he grew it in practically pure culture from both lungs of one case at autopsy. Synnott and Clark in Camp Dix found streptococci and pneumococci predominating, and, although making no particular effort to study the B. influenzæ or determine its frequency, they found it in the majority of cases when it was looked for. Blanton and Irons reported as follows from Camp Custer. From cultures of the nose and throat of 357 examined before the epidemic struck, B. influenzæ was found in 5.1 per cent.; in 366 throat cultures of influenza cases without physical signs of pneumonia the same organism was grown in 44, or 8 per cent.; sputa typed for pneumococci 740 times from influenza cases with pneumonia gave isolations of B. influenzæ 38 times, or 5 per cent.—8 times alone, but here it should be remarked that these latter isolations were only attempted after the organism was suspected from the morphological picture of the smears; from 280 autopsies B. influenzæ was recovered 8 times from the lung and 3 times from the heart’s blood. This report covered the period from the outbreak of the epidemic, October 5 (or as given by Soper, September 30) to October 22, at the outside a period of 22 days. During this time 366 throat cultures, 510 blood cultures, 740 sputa typed for pneumococci, 280 autopsies with cultures from both lung and heart’s blood, made a total of primary cultures of well over 2,000. The technical difficulties would make it almost impossible to handle such a mass of material and get reliable results for the incidence of B. influenzæ.

Brem, Bolling and Casper in Camp Fremont found B. influenzæ in 259 from 537 selected cases in swabs from the nasopharynx. It was also noted in a fair number of other examinations. Opie and his co-workers found B. influenzæ to be very frequent at Camp Pike. Spooner, Scott and Heath isolated B. influenzæ at Camp Devens from the sputa of 104 cases, from nasopharyngeal swabs in 11 out of 18 attempts and from the pleural fluid 8 times out of 45, twice pure. From 37 autopsies they found B. influenzæ in 23 and in pure culture in at least 1 lobe of the lung in 16. From 82 blood cultures at autopsy B. influenzæ was recovered twice. Nichols and Stimmel studied lung punctures during life and grew the B. influenzæ from 7 out of 10 attempts, 5 times in pure culture. Stone and Swift at Fort Riley found B. influenzæ in 18.7 per cent. of 928 sputa and in 5.2 per cent. of 77 sputa from fatal cases. He recovered it from autopsy material; 21 times from 51 lungs, once alone; twice from 26 pleural fluids; twice from 30 heart bloods; 19 times from the sinuses of 40, and 9 times from the ear and mastoid of 17 cases.

Lamb and Brannin at Camp Cody examined 80 typical cases early in the epidemic. They found B. influenzæ predominated in 46 per cent. being present with pneumococci on 41 per cent. of the plates. They also grew the influenza bacillus from a fair number of other cases.

Wollstein and Goldbloom in the Babies Hospital of the City of New York found the B. influenzæ in 13 of 17 sputa during life and in both lungs of all 18 autopsies as well as in the heart’s blood of one. Kotz found it in half of his 30 cases. Pritchett and Stillman grew the influenza bacillus from 41 of 49 cases of influenza, from 40 of 43 cases of influenza with broncho-pneumonia, from all of six other broncho-pneumonia cases and from 11 of 20 cases of lobar pneumonia, making a total of 98 positive findings from 118 or 82 per cent. They further found 25 positives from 54 convalescent and 74 from 177 normal sputa. Wolbach found this organism in pure culture in one or more lobes of the lungs of 9 from 23 cultured cases. It was demonstrated in 23 of 28 either by culture or in section.

Similar results are to be found in reports from Great Britain. Martin noted a great increase in the numbers present as the sputum became more purulent. Hicks and Gray found B. influenzæ by culture in 75 per cent. of their cases. They were seen in direct smears in only 70 per cent. Gotch and Wittingham considered M. catarrhalis to be the etiological factor as it was found in all of their 50 cases. B. influenzæ was grown in 8 per cent., although B. influenzæ-like bacilli, were seen in 62 per cent. of their smears. Averill, Young and Griffiths studied the sputum from 41 cases and found B. influenzæ in 32. It is interesting that Macdonald and Lyth determined the incubation period to be 41 hours as a minimum in their own experience and that from the posterior nares of one of them B. influenzæ was obtained.

Schofield and Cynn found the B. influenzæ in Korea. Kraus in Brazil found it in the sputum in 62 per cent. of his cases of influenza. It was also found in the organs of 27 who had died, being in pure culture in five. It has further been found in France, Italy and practically all parts of the world where investigations have been made. The German literature is at present only available in the report of the British Medical Research Committee which is written in a more or less popular manner with a rather strong tendency against the importance of B. influenzæ. Dietrich, Simmonds, Bergmann and others, however, found B. influenzæ rather frequently. Such quotations as “Uhlenhuth, a diehard of bacteriologic orthodoxy, has clearly shown signs of uneasiness” and “one empyema and one throat swab yielded the looked for growth” will indicate why this review is of little use. It is certainly necessary to “look for” the B. influenzæ to get results of any worth.

Secondary, ancillary or symbiotic bacteria are of cardinal importance in these infections. It has been considered by some writers as characteristic for the influenza bacillus to be followed so frequently with such a variety of secondary invaders. Sahli looked upon the complex of B. influenzæ, pneumococcus and streptococcus as the true etiological cause of influenza. Abrahams and his associates discussed the symbiotic effect of the B. influenzæ in raising the virulence of pneumococci previously present in the patient and many other investigators lay stress on these symbiotic relationships.

Pneumococci appear to be the commonest of these secondary micro-organisms judging from the various published reports, but the fact must not be overlooked that, particularly in America, the typing of pneumococci has drawn a disproportionate attention to this group. Hemolytic streptococci have received much attention (Ely and his co-workers and several others). M. catarrhalis (Gotch and Wittingham and several of the British writers), members of the B. mucosus capsulatus group (Nichols and Stimmel, Rucker and Wenner), staphylococcus aureus (Patrick), various ill-defined streptococci (Rosenow and several British writers), capsulated cocci apparently different from pneumococci, B. pestislike forms and many others have been given more or less attention, often as clearly recognized secondary infections, but not infrequently as of primary significance.

B. influenzæ, however, is the organism most regularly found in this pandemic where carefully looked for, and the evidence of its lowering the general resistance to bacterial invasion is very strong. The experiments of Ghedini and Fedeli showing the effect of the toxine on muscular tone and those of Ghedini and Breccia who found a similar effect on blood vessels are worthy of note.

The fact that the flora differs so widely in various regions is what one might expect and many investigators have emphasized the significance of this. Bacteria in the mouth and throat are readily transmitted from individual to individual and under the conditions in the training camps and our modern life, the development of local flora is not surprising. That it is of very great importance is recognized by all and it is often a determining factor in the severity of the infection. Nevertheless, influenza in this pandemic has been almost equally severe whatever the secondary organism may have been.

I have discussed in another place the suggestion of the stimulating effect of various bacteria on the growth and toxine production of B. influenzæ. Huntoon showed the effect of hemolytic streptococci in cultures to be helpful in toxine production. An important point, however, is that no one bacterium has been shown to be exclusive in thus affecting the growth on media of the influenza bacillus, and in the animal experiments in raising the invasive and pathogenic power of this organism the same appears to be true. The infection in influenza, in the vast majority of cases, rapidly becomes a mixed one. The secondary organisms at times completely dominating the field, at least as far as numbers go, most frequently invade the blood stream and it would appear often play the important role in many of the secondary conditions.

_Chronic Infections_

B. influenzæ is a frequent finding in the sputum of patients with chronic bronchitis, pulmonary tuberculosis and other chronic conditions in the respiratory tract. Boggs recovered this bacillus from two cases of bronchiectasis, Richards and Gurd had a similar case and Tedesko reported several. The literature is filled with references to the finding of B. influenzæ in cases of chronic bronchitis. Those reported by Lord, Madison and Tedesko quoted above will serve as examples. The frequent positive cultures in cases of pulmonary tuberculosis so often referred to in reviews of the literature and the significance of these findings, as pointed out by Scheller, are important as bearing on the much debated subject of the effect of influenza on this disease. These types of chronic infection by the influenza bacillus should be more generally recognized as they undoubtedly will become more numerous following this last epidemic if we can judge from the experience of the past.

_Infections of the Pleura_

The recovery of B. influenzæ from the pleural cavity is not uncommon as is shown in the above review. The findings of MacCallum, Cole and others during the spring of 1918 are particularly interesting. Beall in 1906 reported a case of empyema with large quantities of green pus in which B. influenzæ was found in pure culture.

_Sinuses of the Head_

Infection of the accessory sinuses of the head has long been recognized as occurring in influenza. Frankel found B. influenzæ in 4 from 40 infected antra. Lindenthal, who was particularly interested in the question of sporadic influenza, found the bacillus in one or more of the head sinuses in six of eight carefully studied cases. He considered that the B. influenzæ remained in these areas during inter-epidemic times and from hence caused the sporadic outbreaks of influenza. Howard and Ingersoll reviewed the literature up to 1898 and grew B. influenzæ from one of three acute antral diseases. They did not find it, however, in 12 chronic cases. Clemens believed the influenza bacillus to be present in the sinuses rather frequently in cases where it was overgrown or difficult to culture from the lower respiratory secretions. Moszkowski grew it in one case from the pus of the antrum. Tedesko recorded several positive results and many others are reported in the literature.

The two cases reported by Lacy (1918), the findings during the present epidemic by Stone and Swift of B. influenzæ in 13 of 28 sphenoidal and 6 of 12 ethmoidal sinuses cultured at necropsy, those by Spooner, Scott and Heath, of B. influenzæ in four frontal sinuses and in eight sphenoidal, and the recovery by Wolbach of B. influenzæ in cultures from the sinuses in certain cases where the lung cultures were negative, emphasize the importance and frequency of the infection by this organism in these cavities. Keegan, who laid particular stress on lung punctures and autopsy examinations, pointed out that in throat cultures the probability that the influenza focus is often not in the pharynx but in some recess of the nasal cavity.

H. E. Robertson in the spring of 1918 reported the infection of the sinuses in seven cases of tracheo-bronchitis with patches of broncho-pneumonia and the growth of B. influenzæ from sphenoid, ethmoid or frontal sinuses of all these cases. He also found this organism in the sphenoid of six cases dying with various diseases as well as in two accident cases with death under 24 hours. The importance of these results was laid stress on by the author, not only on account of the probable toxic absorption and the general menace of spread, but, more particularly, because such individuals, acting as carriers, could furnish foci for the spread of epidemics.

_Eye and Ear_

Infections of the eye by the influenza bacillus are quite common. This subject is fully discussed by Axenfeld (text-book, “The Bacteriology of the Eye”). Giani and Picchi found it in the eye in 66 per cent. of influenza cases, in 90 per cent. of epidemic conjunctivitis, and in the normal eye of 5.8 per cent. Wynekoop, in 1903, reported having found this organism in cases of conjunctivitis in 1899. Guiral, in the recent epidemic, found influenza bacillus constantly present in the secretions in cases of what seemed to be Week’s conjunctivitis. Ulceration of the cornea was rather common. One such case is mentioned in which there was no pain in the eyes, but general symptoms of influenza. The middle ear is also sometimes infected. Between the report of Kossel in 1893 and that of Stone and Swift in 1918, who found the middle ear and mastoid to contain B. influenzæ in 8 of 17 cases, there have been many references in the literature to this complication by the influenza bacillus. The evidence indicates, however, that in the middle ear, as in the pleural cavity, the secondary bacteria are far more often the important ones.

_Meninges_

Influenzal meningitis seems to stand by itself as a manifestation of the pathogenic effects of B. influenzæ. The literature is too voluminous to review in this place, but the evidence would seem to point to a more invasive and pathogenic type of this organism, if not to a separate member of the group.

_Invasion of the Blood Stream_

The evidence in clinical influenza would suggest at times a bacteremia in addition to the severe toxemia, which is such a constant feature of the disease. Simultaneously with the discovery of B. influenzæ, Canon reported finding bacilli of similar morphology in blood smears, but was unable to grow them, and it would appear at least doubtful that he was dealing with the influenza bacillus. Meunier is probably the first who grew this organism from the blood. He recovered it from 8 blood cultures out of 10 in cases of broncho-pneumonia following measles, and in one other case of broncho-pneumonia. A very full discussion of this question is to be found in Canon’s book on “The Bacteriology of the Blood in Infectious Diseases.” Of particular interest are the results of Ghedini, who made a careful study of 28 influenza patients. B. influenzæ was grown from the blood in 18 of these at the height of the fever, while in the 10 negative cases the disease was milder or the blood was taken only after the temperature had fallen. The amount of blood used was 20-30 c.c., and it was cultured in lecithin broth. In practically all of his cases several cultures were taken, and in a number of the positive cases negative results were obtained both before and after the acme of the fever. He also grew the bacillus from 8 of 14 spleen punctures of these patients. Madison (1910) reported the recovery of this bacillus from the blood of a patient with a primary broncho-pneumonia who recovered. This author also used about 30 c.c. of blood. Thursfield, in 1910, also reported two cases of B. influenzæ bacteremia in which the organisms were recovered at the height of the temperature. One had influenza, the other phlebitis, and both recovered. Tedesko and several others have found it in the heart’s blood in many cases, more especially in broncho-pneumonia after measles.

During the present epidemic the positive cultures of this bacillus from the blood have been rather infrequent. J. S. Fleming had 2; 2 are quoted in the report of the Influenza Committee of the Advisory Board to the D. G. M. S. (Peters and Cookson); Medalia had 2 during life and 19 of 34 at autopsy; Orticoni, Barbie and Leclerc in 5 of 10 blood cultures in one series, and 7 of 19 in another; Stone and Swift 2 at autopsy; McKeekin, in Australia, influenza-like bacilli in 4; Blanton and Irons three times in the heart’s blood, one of these pure; Spooner, Scott and Heath twice in the heart’s blood at autopsy, and Wollstein and Goldbloom from the heart’s blood in one child. In the majority of these findings the bacillus was not found in pure culture. Abrahams and his associates found the B. influenzæ along with a pneumococcus and M. catarrhalis from the heart’s blood in one case. In our positive blood culture there was evidence of the same mixture being present.

Before drawing sweeping conclusions against the invasion of the blood by B. influenzæ it must be remembered that the quantity of blood used has been generally only about 10 c.c., and often much less, the difficulty of observing growth if the culture is pure has been largely overlooked, the use of more favorable media than blood agar and the possible inhibitory action of influenzal blood, as suggested by Wittingham and Sims, Rivers and others, has not been considered, and further that sufficient care has not been exercised to obtain blood at the most favorable period in the disease. It may be recalled that the problem is quite similar to that of demonstrating the organisms in the blood in patients with streptococcus viridans bacteremia.

All the available evidence, however, points to the invasion of the blood in influenzal infections as being a very fleeting one. Unless this is true, it would be surprising in the many hundreds of blood cultures which have been taken in the concentrated study of patients during the recent pandemic, if more successful cultures had not been obtained. General infections with localization of B. influenzæ in different parts of the body are here of interest—such as that reported by Slawyk and others. Whether the strains causing meningitis, and which apparently more frequently invade the blood, are really different members of the hemophilic group or only forms with a higher invasive power is still, I believe, an open question.

_Endocarditis_

In endocarditis the B. influenzæ is probably, after streptococci, the organism most frequently isolated from the blood. Rosenthal from heart’s blood at autopsy, Schlangenhaufer, Jehle two cases, Horder (1907) six cases, and who believed he was the first to isolate B. influenzæ from the blood, Tedesko in a number at autopsy, Spat, F. J. Smith, Saathoff, Libman four cases, Sacquepee, McPhedran, Mann, Rainaford and Warren three cultures from two patients, and a number of others all bear witness to its frequency.

Other organs of the body are sometimes found to contain B. influenzæ. Adrian, Schultes, Basile and Tedesko have all recovered this organism from the diseased appendix. Several years ago a bacillus, considered, to be B. influenzæ, was grown from the pus of an appendix abscess in our laboratories. Wright found it in pyelonephrosis. Klieneberger found influenza-like bacilli in cases of cystitis. Menko reported the bacillus from orchitis, and Cohn found numerous influenza-like bacilli in the discharge from urethritis. Meunier found it in pure culture in a case of osteoperiostitis. Huyghe, Besancon and Griffon recovered it from infected joints, as did Pacchioni in a general infection. Weil found it in the pus about the hip joint one month after an attack of influenza. This short review serves to illustrate that the influenza bacillus, although generally limited to infections in the respiratory tract, is, nevertheless, capable of infecting other parts.

_Immunity—Phagocytosis_

Phagocytosis of the B. influenzæ has been very frequently noted in the study of sputum smears. It has been observed, moreover, that this phenomenon occurs most frequently when the patient is on the road to recovery (Pfeiffer, Martin, and others), and it may indicate an important reaction on the part of the body to this organism. Tunnicliff in a recent report, however, did not find the opsonic index to be raised above the normal in her patients, and Tunnicliff and Davis had difficulty with a spontaneous phagocytosis of this bacillus. This difficulty was to a large extent absent in her later study.

_Agglutination_

Agglutination tests have been used by many investigators in attempts to determine a specific reaction in the sera of persons suffering from influenza. Such reactions develop, as we know, against secondary infecting bacteria, so that unqualified conclusions cannot be drawn that agglutinins in the sera of patients against B. influenzæ indicate the etiological importance of this organism. Vagedes using a dilution of 1-50 found 8 positives among 27 patients tested. Lord found the test most inconstant. Ghedini obtained useful results by using serum in dilutions 1-20 to 1-30, and had 17 positives from 28 influenza cases. He found agglutinins present three to four days after the height of the infection, and noted that the sera became practically normal after three to four weeks. Fichtner, although he obtained agglutination with sera of influenza patients in high dilutions (1-100 and 1-750), found his controls were often agglutinated, and consequently drew no conclusions. Wollstein (1906) did a series of agglutination tests, using various strains of B. influenzæ. The sera of patients she found very unsatisfactory, but by immunizing rabbits with this organism she obtained sera with titres up to 1 in 400. She could find no differences among the various strains studied. Somewhat similar results were obtained by her in 1915 working with strains from the meninges and the respiratory tract. Odaira carried out a rather extensive series of tests, using immunized rabbit sera and a special method of making his bacterial emulsions. He was able to distinguish B. influenzæ from both B. pertussis and the so-called Cohen’s bacillus of meningitis. Friedberger’s dog bacillus, however, could not be differentiated from B. influenzæ by this means. A. Fleming during the recent epidemic had good results with the sera of 21 patients. He incubated at 50° C. for two hours. He also used sera of immunized rabbits and got marked agglutination against the homologous strain, but varying results with other strains. He noted some strains agglutinated readily, while others did not. Eyre and Lowe noted an increase in agglutinins in the sera of people vaccinated against the influenza bacillus. Couret and Herbert could distinguish two types and a possible third among their strains. Park and his co-workers found numerous types by means of agglutination. Absorption of agglutinins was found helpful by these last two workers. There are so many factors capable of altering the sensitiveness of bacteria to agglutination, as in the well-known experiments of Neufeld, that we must recognize that much work is still to be done before we can properly interpret the results of these agglutination tests.

_Binding of Complement_

Complement fixation tests were carried out by Odaira but his results were much less satisfactory than those he obtained by means of agglutination. Rapaport made an extensive study of this test, using the sera of patients in various stages of convalescence. Three hundred and fifteen convalescents showed 54.5 per cent. positive while 300 controls only gave 9.5 per cent. positive results. Most of the positive cases were in patients three to five days after their illness, but the reaction was found in convalescents after from 1 to 45 days. Sera from acutely ill patients at times showed negative or slightly positive reactions but these same sera after keeping for some days and retesting often gave strongly positive results. This would appear to be a promising field for investigation.

_Anaphylaxis_

Hypersensitiveness was noted by W. F. Robertson in chronic infections with B. influenzæ. Wollacott in a letter to the British Medical Journal suggested that the severity of the recent outbreak of influenza may possibly be due to the development of a state of anaphylaxis. There would seem to be at least some evidence in favor of such a view in the fact that the severe outbreak was preceded by epidemics of a milder form of influenza and that the influenza bacillus was probably widely spread during this time. Greenwood, as quoted above, noted that primary cases always precede the mass attack. Of course, the term anaphylaxis has been used to explain almost everything. Nevertheless, the theory is interesting. The skin tests which we did for hypersensitiveness were, as I have noted above, negative but there is a possibility that the failure of the reaction may indicate a higher resistance or even an antitoxin, now that the bacillus can be classed as a toxicogenic one. Anti-influenza sera have been produced by a few investigators (Latapie, Wollstein) but have not found any practical application during this pandemic. Vaccination is discussed elsewhere in these studies.

_Experiments on the Human_

There has never been in the history of medicine so many experiments on human beings as have been carried out in the attempts to discover the etiological factor in the recent pandemic of influenza. Davis has called attention to a successful human inoculation with pure cultures of B. influenzæ which he performed in 1906. During the present investigation at least 200 men have volunteered as experimental subjects, and the results of many different methods of attempting to transmit the disease, have been disappointing and inconclusive. I will not attempt to review the reports at present available, as a great deal of the work done has not yet appeared in print. The important point is that the results do not affect the various views held as to the causative agent in pandemic influenza nor the massive evidence for transmission of the disease under natural epidemic conditions.

It is my opinion, as expressed above, that practically all of the population are rapidly infected during such a pandemic as we have had. The resistant have escaped, and it would appear to be very difficult to break down this resistance. The human experiment carried out by Pettenkofer on himself and his assistant with vibrion choleræ is an example, but we have numerous others demonstrating the same kind of phenomena in most of our diseases of established bacterial origin. In diphtheria we have an explanation in the varying antitoxic content of the sera, but we really know very little of what are the actual factors in preventing or determining infection among exposed individuals in the natural history of most diseases. The reports of Leonard Hill and Gregor are well worth reading in this connection, as well as the editorial in the same number of the British Medical Journal. We are not in a position to be very dogmatic on the causes of epidemics. The mere presence of the bacteria or any other living virus is not in itself sufficient to explain the phenomenon, and one of the chief objects of this paper is to indicate from the collected facts, that in the words of Flexner, “the case against the influenza bacillus is not proved.”

_Conclusions_

1. B. influenzæ is one of a group of hemophilic bacteria and there are probably strains of this organism which may be differentiated which will lead to further subdivisions of the group.

2. B. influenzæ as we understand it today, is distinguished by its morphological and staining characters; its requiring hemoglobin in some form for its development; its showing symbiotic reactions with other bacteria which stimulate its growth; the production of a toxine and its usual low pathogenicity for animals.

3. The media found most favorable for its growth are those containing blood with the hemoglobin content altered in certain ways, (1) by heating, (2) the addition of various chemicals, (3) by the action of other bacteria or their products. The heated blood agar I have found to be a most efficient and readily prepared medium.

4. Since B. influenzæ is so difficult to isolate, it is necessary to be very cautious in interpreting results unless the greatest effort has been made to demonstrate the presence of this organism.

5. B. influenzæ should be considered, from the evidence at hand, as the bacterial causative agent in epidemic influenza, and it should be recognized that secondary infections following the primary attack by this organism are both frequent and important. This view I believe the logical one, unless much more convincing evidence than we have today may demonstrate another more probable living virus as the cause.

6. B. influenzæ is a frequent etiological factor in purulent and chronic bronchitis, broncho-pneumonia and other acute and chronic respiratory infections, in meningitis, endocarditis, sinusitis, conjunctivitis and other conditions, as well as in complications of many other diseases.

7. There are many carriers of the bacillus among our population, both in apparently normal individuals and in those suffering from chronic infections of bronchi, sinuses or other parts.

8. The problem of what constitutes resistance or susceptibility to this infection are as far from solution as they are in most other respiratory diseases, and the attempts to explain the reasons for epidemics have been as futile as they are for meningitis and many other respiratory epidemics.

9. It would not appear that the immunological reaction against this infection has been discovered, but the possibility of its being of an antitoxic nature opens an interesting field for investigation.

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