286 . CLINICAL BACTERIOLOGY. 



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 exten- 

 sive epidemics of influenza domestic animals escape the dis- 

 ease. 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 in- 

 fluenza, 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 influenza- 

 culture 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 depres- 

 sion of temperature (to 32.2 C. 90 F.) ; under these 

 circumstances the symptoms are probably the result of in- 

 toxication. Symptoms of intoxication (fever, muscular 

 paresis) also appeared in rabbits after intravenous injection 

 of considerable amounts of bacteria. Further, cultures de- 

 vitalized by chloroform proved quite toxic. The influenza- 

 bacillus 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 re- 

 acted much less vigorously to a second injection of influenza- 

 bacilli 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 



