2l6 INFLAMMATORY AND SUPPURATIVE CONDITIONS. 



Now, if such a partly attenuated culture be injected sub- 

 cutaneously into a rabbit, there is greater local reaction ; 

 pneumonia, with exudation of lymph on the surface of the 

 pleura, and a similar condition in the peritoneum, may occur. 

 In sheep greater immunity is marked by the occurrence, after 

 subcutaneous inoculation, of an enormous local sero-fibrinous 

 exudation, and by the fact that few pneumococci are found in 

 the blood stream. Intrapulmonary injection in sheep is fol- 

 lowed by a typical pneumonia, which is generally fatal. The 

 dog is still more immune ; in it also intrapulmonary injection is 

 followed by a fibrinous pneumonia, which is only sometimes fatal. 

 Inoculation by inhalation appears only to have been performed in 

 the susceptible mouse and rabbit; here also septicaemia resulted. 



The general conclusion to be drawn from these experiments 

 thus is that in highly susceptible animals virulent pneumococci 

 produce a general septicaemia ; whereas in more immune species 

 there is an acute local reaction at the point of inoculation, and 

 if the latter be in the lung, then there may result pneumonia, 

 which, of course, is merely a local acute inflammation occurring 

 in a special tissue, but identical in essential pathology with an 

 inflammatory reaction in any other part of the body. When a 

 dose of pneumococci sufficient to kill a rabbit is injected sub- 

 cutaneously in the human subject, it gives rise to a local inflam- 

 matory swelling with redness and slight rise of temperature, all 

 of which pass off in a few days. It is therefore justifiable to 

 suppose that man occupies an intermediate place in the scale of 

 susceptibility, probably between the dog and the sheep, and that 

 when the pneumococcus gains an entrance to his lungs, the 

 local reaction in the form of pneumonia occurs. 



Analogies to the facts just stated are afforded in the case 

 of other diseases caused by bacteria. Thus, for example, the 

 anthrax bacillus produces in the human subject more marked 

 inflammatory reaction, and is more restricted to the local 

 lesions, than in the much more susceptible guinea-pig, in which 

 it produces a rapidly fatal septicaemia. An analogous result is 

 also obtained when, instead of taking animals of different sus- 

 ceptibility, the same species of animal is used, but the virulence 

 of the organism is altered ; for example, a streptococcus, as 

 already stated, producing at one time an erysipelatous condition, 

 causes an acute septicaemia when its virulence is increased. 



