In the bacteriologic diagnosis of influenza we must remember that, unfortunately, there exists also the pseudo influenza bacillus. In three cases of diphtheric bronchopneumonia Pfeiffer found in the smear preparations "numerous fine rods which, from their form and staining properties, could hardly be distinguished from the influenza bacilli, which they resembled also culturally, since they grew only upon blood agar and formed colonies which resembled the influenza colonies in the minutest details." For the extremely subtle points of difference between these confusing " pseudo influenza bacilli" and the "genuine" ones we must refer our readers to the original treatise.*
Opinions differ regarding the presence of influenza bacilli in the blood. Canon asserts that he found them in the blood taken from the fingers of 20 patients " in nearly all cases Klein (London) found them only 6 times among 43 fresh cases; Pfuhl, in several cases, also obtained positive results. [According to Jehle, the bacilli appear in the circulation particularly in the cases where influenza occurs as a secondary infection to one of the exanthemata. His observations were made on the heart blood after death. Slawyk records the case of a child of nine months, in which he found the bacillus in the circulation a few hours before death.-Ed.] On the other hand, Pfeiffer and Beck never found the bacilli in the blood, either microscopically or in cultures. Pfeiffer, however, twice saw isolated influenza bacilli in the veins in microscopic sections, and he was able several times to cultivate a few colonies from the spleen and kidneys.
The fact that the influenza bacilli are but rarely found in the blood does not prove that they do not enter the circulation. It is the same with influenza bacilli as with many other micro organisms whose demonstration in the blood has either been unsuccessful or has succeeded only occasionally. The numerous organic lesions (inflammations) point to the transportation of the suspected microbes by the blood, and the actual discovery of the specific bacillus in the affected areas demonstrates its etiologic significance. On the other hand, the presence of influenza bacilli in the tissues of various organs has not been satisfactorily proved.
Pfeiffer found crowds of the bacilli under the pulmonary epithelium in patients suffering from influenza pneumonia, but only very few in the submucous connective tissue. A. Pfuhl found the small rods in several cases of influenza encephalitis, partly in the membranes and partly in the substance and fluids of the central nervous system, but always within the blood vessels or perivascular lymphatics. He also found them in areas of softening of the brain and spinal cord; in a cerebellar abscess; both microscopically and culturally in an area of softening in the cerebellum; in the blood, and in the aqueous humor; in smear preparations from the liver, spleen, and kidneys; in sections of the brain in whose capillaries they were found both isolated and forming quite extensive thrombi; and, finally, in sections from the liver, partly within the capillaries, partly free in the tissues, and in accumulations of detritus. A further contribution to this question is that of Nauwerck, who, in a case of influenza encephalitis, found micro organisms similar to Pfeiffer's bacilli in sections of the cerebellum, which was the organ chiefly affected, in the apoplectic areas of the cerebellum, in the adjoining hemorrhagic area of softening, in the perivascular lymph spaces, but not in the blood vessels. The cultures, too, resembled and were probably identical with those of the influenza organism.
* "Zeitschr. f. Hyg. u. Infectionskrankh.," Bd. xiii, S. 383.
All attempts to produce typical influenza in animals by inoculation, either of richly infected sputum or of pure cultures of influenza bacilli, have failed. In particular it has been impossible to demonstrate any increase of the inoculated influenza bacilli in the body of the animal [except when injected intra peritoneally.-Ed.]. Pfeiffer, it is true, succeeded in causing general and local symptoms of the disease in monkeys (namely, fever, and once, by intratracheal inoculation, a retrotracheal abscess with purulent bronchitis, in which a few dead influenza bacilli were found. By giving large doses he was able to kill monkeys and rabbits which manifested severe "symptoms of poisoning " due to the intoxication caused by the simultaneous inoculation of "influenza toxin" with the bacilli. [This occurred even when killed cultures were used. The symptoms (dyspnea and muscular weakness) bore sufficient resemblance to those in man for justifying the deduction that the influenza toxin is chiefly concerned in this production. In animals, inflammatory conditions can be produced by painting mucous membranes, especially if injured, with cultures, and particularly in the osseous system after injury, also otitis media. The bacillus can be recovered from the lesions (Perez). Repeated injections of toxins do not lead to the production of an antitoxic or bacterial serum, and the animals used will succumb to a larger dose of culture.-Ed.]
Klein (London) made inoculation experiments with influenza sputum containing many bacilli, and also with pure cultures of the organisms, upon 24 monkeys, by means of subcutaneous and intratracheal inoculation; the results were consistently negative. Only in one monkey which died of pneumonia were Pfeiffer's bacilli found, as well as other microbes.
The best proof of the immunity of monkeys toward human influenza seems to me to be afforded by the fact that these animals in the monkey house of the zoologic gardens in London showed no signs of the disease, although in the influenza period they were visited by thousands of persons and must certainly have been coughed at by innumerable ambulatory influenza patients. It will be appropriate to consider here the much discussed controversial question of influenza of domestic animals.