the disease is quite considerable; further, that the disease appears in many cases in the form of a mild coryza and of a harmless bronchial catarrh, and these at the beginning of the epidemic are not immediately recognized as influenza; that even after the epidemic character of the disease is established they do not confine patients to the house, so that opportunity is thus afforded, in sneezing and in coughing, to disseminate innumerable influenza-bacilli among those not yet infected. The sudden recrudescence of apparently extinct epidemics is rendered comprehensible by the fact just mentioned, that there are cases of chronic influenza that act for a long time as carriers of bacilli capable of inducing influenza.

Experiments on Animals.-Even in the most extensive epidemics of influenza domestic animals escape the disease. Success in the transmission of influenza-bacilli to animals was therefore improbable from the outset. Pfeiffer undertook experiments on mice, rats, guinea-pigs, rabbits, swine, cats, dogs, and monkeys. Only in the last-named animal was it possible to induce an infection resembling influenza, and then only by introducing the bacteria through the chest-wall directly into the lung, and also which was more important—in a monkey, by introducing an influenzaculture into the uninjured nose. The disease manifested itself by some cough and fever of several days' duration. Multiplication of the inoculated bacteria was, however, not observed. By introducing large amounts death can be caused in rabbits quite rapidly, with antemortem depression of temperature (to 32.2° C.-90° F.); under these circumstances the symptoms are probably the result of intoxication. Symptoms of intoxication (fever, muscular paresis) also appeared in rabbits after intravenous injection of considerable amounts of bacteria. Further, cultures devitalized by chloroform proved quite toxic. The influenzabacillus thus appears to generate an active toxin, a fact that sheds considerable light upon the nervous manifestations frequently observed in cases of influenza in human beings.

Immunity. The monkeys in Pfeiffer's experiments reacted much less vigorously to a second injection of influenzabacilli than to the first; and Pfeiffer believes this to be an indication of immunity. Human beings certainly can be attacked several times by influenza, even in the course of the same epidemic. This fact does not, of course, exclude the possibility that a certain degree of immunity follows an

attack of influenza, but this must, however, be considered as only temporary.

Pseudo-influenza-bacilli.-In a number of bronchopneumonic foci in patients not suffering from influenza (but from diphtheria) Pfeiffer found bacilli that in form and staining properties resembled influenza-bacilli, and that, like these, developed exclusively upon blood-agar. Similar bacilli have since been isolated by various observers from cases of otitis media and of influenza. Pfeiffer believes these organisms to be related to influenza-bacilli, and he designates them pseudo-influenza-bacilli. They are to be distinguished from true influenza-bacilli by culture, in which, after the lapse of twenty-four hours, they appear considerably larger in all dimensions, and they exhibit a marked tendency to the formation of long pseudo-filaments. In similar cultures of the true bacillus the latter are wanting entirely or appear but exceptionally.

Bacteriologic Diagnosis of Influenza.-The bacteriologic diagnosis is made from examination of the sputum derived from the deepest possible portions of the airpassages, and thus preferably from examination of the bronchial sputum. Microscopic examination alone is usually insufficient, but, as a rule, cultivation of the bacillus is necessary, the method for which has already been described in detail (p. 283, Plate-procedure). Bacteriologic examination may acquire differential diagnostic significance. Thus, Borchardt relates a case in which the diagnosis oscillated for a long time between typhoid fever and influenza, until bacteriologic examination decided in favor of the latter.

ANTHRAX.

Pollender, in Germany, in 1849, and Rayer and Davaine, in France, in 1850, were the first, independently of each other, to detect bacilli in the blood of animals suffering from anthrax. The growth of the anthrax-bacillus in pure culture and the experimental development of the disease by means of the bacillus were successfully accomplished first by Koch in 1876.

Morphology of the Anthrax-bacilli.-Anthrax-bacilli appear as transparent, homogeneous, nonmotile rods. are from 1 to 1.5 μ thick, and from 5 or 6 to 10 long, but they

They

are subject to great variations in size. In cultures the bacillus is prone to be considerably longer than in the animal organism. In the blood of human beings it is shorter than in that of rodents; in cattle it is shorter than in white mice and in guineapigs. The broad side of the bacillus is slightly rounded. The surfaces of two adjacent bacilli in direct contact are, however, plane. In the blood of animals suffering from anthrax the bacilli are at times collected into small filaments of two or four, or at most five, members. Only attenuated bacilli, just capable of causing death in experimental animals, form long filaments in the organs of the animals. Such filaments are usual in the body of the frog. In cultures, on the other hand,

the anthrax-bacillus exhibits an especial tendency to the formation of long, intertwining chains. Frequently, bacilli obtained from the lesions of the disease present a bright border that some observers have looked upon as a capsule. This supposed capsule may be demonstrated by the staining method of Johne in the following manner: The preparation made from the blood or visceral fluid and dried in the air is passed three times through the flame; stained for from fifteen to thirty seconds in a slightly warmed, two per cent. aqueous solution of gentian-violet; washed in water; exposed for ten minutes to the action of a one per cent. solution of acetic acid; and examined in water. It is important to make the examination in water, as the mucoid capsule is not visible when the specimen is

mounted in Canada balsam. The bacillus can be stained with all aniline dyes and also by the method of Gram.

Cultivation of Anthrax-bacilli.-The anthrax-bacillus is extremely indifferent with regard to its nutrient material. It will develop in the absence of oxygen, but it does not then generate a peptonizing ferment. The temperature-minimum is 12° C. (53.6° F.); the temperature-optimum, 35° C. (95° F.); the temperature-maximum, 45° C. (113° F.).

On gelatin-plates, with a magnification of from 80 to 100, the superficial colonies appear as round discs of yellowish color, constituted of a tangle of threads which form a dense, impenetrable convolution at the center. Especially the border presents

quite distinctly this filamentous structure, and from it frequently passes off a delicate network of convoluted and curled processes, which gives the colonies their characteristic appearance. The gelatin in the neighborhood is softened, and begins slowly to undergo liquefaction.

In gelatin stab-cultures the line of inoculation forms a whitish band, from the circumference of which numerous ramifying processes extend into the gelatin. Liquefaction of the culturemedium progresses slowly, the nonmotile bacilli, by reason of their weight, sinking to the bottom of the liquefied area.

In bouillon small fragments appear and fall to the bottom; they represent a union of the anthrax-bacilli for the formation of convolutions of filaments.

On agar-agar a dense, creamy, coherent deposit forms; and upon potatoes a dry, whitish-gray layer. Blood-serum is liquefied. Milk is coagulated and peptonized.

Sporulation. If anthrax-cultures are exposed to temperatures above 18° C. (64.4° F.), the bacilli soon exhibit sporeformation. Slight development of spores takes place, besides, down to the temperature-minimum. The anthrax-spore invariably lies exactly in the middle of the mother-cell, being much shorter, but as wide, and possessing an oval shape. After a time the germinating bacillus disintegrates, and the spore is set free. If the spore is introduced into a sterile hanging drop of bouillon, gelatin, or agar, its germination can be accurately followed under the microscope (possibly with the employment of a warm stage). The spore first loses its glistening appearance, and increases in volume. Its membrane then ruptures at one extremity and permits the escape of the newly formed bacillus. The young bacillus enlarges in the direction of the long axis of the spore, and soon throws off the still adherent spore-membrane. Spore-formation takes place only in the presence of free oxygen-thus never in the animal body and never in the uninjured cadaver.

The higher the temperature the more rapidly do the spores develop at 37° C. (98.6° F.), as early as twenty hours; at 21° C. (69.8° F.), not before seventy-two hours; while above 42° C. (107.6° F.) the anthrax-bacilli do not generate spores at all. It is possible artificially to deprive the anthrax-bacilli of their capability of generating spores. For this purpose it is only necessary to add certain antiseptic substances to the nutrient medium (Chamberland and Roux): for instance, carbolic acid in the proportion of from 1 : 600 to I: 1000, potassium bichromate in the proportion of 1: 2000. The bacilli cultivated upon such nutrient media remain sporeless permanently in all subsequent generations, and in this way special asporogenous anthrax-bacilli are developed.

Resistance of Anthrax-bacilli and of Anthrax-spores. -Anthrax-spores, like all other spores, are exceedingly resistant structures; while the fully developed bacilli succumb after exposure for a quarter of an hour to temperatures in the neighborhood of 60° C. (140° F.), the spores die in compressed steam at a temperature of 107° C. (224.6° F.) only after the lapse of five minutes; and in live steam at a temperature of 100° C. (212° F.) only after from twelve to fifteen minutes. Five per cent. carbolic acid destroys the mature forms of anthrax-bacilli in ten seconds, but the spores not before from thirty-seven to forty days. In