BACTERIA IN CROUPOUS PNEUMONIA. 307 



The writer found in his experiments, made in 1881, that in making- a 

 series of inoculations in rabbits the virus increased in virulence, and that, 

 on the other hand, the micrococcus lost its virulence when the cultures 

 were kept for some time. This fact has been verified by the subsequent re- 

 searches of Frankel and of Gameleia. The last-named author has shown that 

 to induce pneumonia in very susceptible animals, like the rabbit, an attenu- 

 ated variety of the microbe should be injected, for the most virulent cul- 

 tures quickly cause death by septicaemia. As he expresses it : "Animals 

 which are too susceptible, like the rabbit and the mouse, do not have pneu- 

 monia, because they do not offer a local reaction ; the virus is generalized in 

 their bodies and they die of an acute septicaemia " 



On the other hand, Gameleia has shown that " animals which are but 

 little susceptible to the pneumonic virus offer a local resistance which gives 

 rise to very pronounced reactionary phenomena (extended fibrino-granular 

 oedema), and consequently they present, as a result of intrapulmonary infec- 

 tion, a typical fibrinous pneumonia. Such animals are the dog and the 

 sheep." 



In his experiments upon these animals Gameleia obtained the following 

 results: 



The sheep was found to survive subcutaneous inoculations, unless very 

 large doses (five cubic centimetres) of the most potent virus were ad- 

 ministered. But intrapulmonary inoculation was always followed by typi- 

 cal fibrinous pneumonia, which in the majority of cases proved fatal. 



The microbe was rarely found in the blood, and successive inoculations 

 from one sheep to another were not successful. Death occurred, after an 

 intrapulmonary inoculation, on the third, fourth, or fifth day. The pneu- 

 monia produced was lobar, and was attended with an extensive fibrinous 

 exudation in which the coccus was found in great abundance. In all, fifty 

 sheep were experimented upon. 



The writer found in his experiments, made in 1881, that the dog resists 

 inoculations with this coccus. Gameleia also obtained negative results when 

 moderate doses were injected beneath the skin, but states that ' ' intrathoracic 

 infection always causes a frank, fibrinous pneumonia which is rarely fatal ; 

 recovery usually occurs in from ten to fifteen days, after the animal has 

 passed through all the stages of red and gray hepatization which character- 

 izes this affection in man." Twelve dogs were experimented upon. 



This micrococcus, then, which in very susceptible animals (mouse, rabbit) 

 invades the blood and quickly causes aeath by septicaemia, when injected 

 through the thoracic walls in less susceptible animals (dog, sheep), or in an 

 attenuated form in the rabbit, gives rise to the local lesions which character- 

 ize fibrinous pneumonia. 



Man comes in the category of slightly susceptible animals, as is shown 

 by the comparatively small mortality from pneumonia, and the fact that the 

 micrococcus found in the exudate into the pulmonary alveoli does not invade 

 the blood, unless in rare instances. We may therefore agree with Gameleia 

 in the following statement : 



"It is clear that the results obtained in the dog and the sheep, animals 

 which have but a slight susceptibility, are most applicable to human patho- 

 logy." 



In my paper read before the Pathological Society of Philadelphia in 

 April, 1885, from which I have already quoted, I say: " It seems extremely 

 probable that this micrococcus is concerned in the etiology of croupous pneu- 

 monia. . . . But this cannot be considered as definitely established by the 

 experiments which have thus far been made upon the lower animals. 1 ' 



The experiments of Gameleia go far toward settling this question in a 

 definite manner, and, considered in connection with those of Talamon and 

 Salvioli, and the extended researches of Frankel, Weichselbaum, and Netter, 

 leave but little doubt that this is the true infectious agent in acute lobar 

 pneumonia. 



