350 PATHOGENIC BACTERIA. 



organism is introduced into a mouse, rabbit, or guinea- 

 pig, the animal dies in one or two days. Exactly the 

 same result can be obtained by the introduction of a 

 piece of the lung-tissue from croupous pneumonia, by 

 the introduction of some of the rusty sputum, and gener- 

 ally by the introduction of saliva. 



The post-mortem shows that an inflammatory change 

 has taken place at the point of inoculation, with a fibrin- 

 ous exudate resembling somewhat that in diphtheria. 

 At times, and especially in dogs, there may be a little 

 pus formed. The other appearances are those of a 

 general disturbance. The spleen is much enlarged, is 

 firm and red brown. The blood in all the organs contains 

 large numbers of the bacteria, most of which exhibit a 

 distinct lanceolate form and have their capsules very 

 distinct. The disease is a pure septicemia unassociated 

 with pronounced tissue-changes. 



In cases of the kind described the lungs show no pneu- 

 monic changes. Likewise, if the hypodermic needle 

 used for injection be plunged through the breast-wall 

 into the pulmonary tissue, no pneumonia results. Mon- 

 ti, however, claims to have found that a true character- 

 istic pneumonia results from the injection of cultures 

 into the trachea of susceptible animals. This observa- 

 tion lacks confirmation. 



Not all animals are susceptible. Guinea-pigs, mice, 

 and rabbits are highly sensitive to the operations of the 

 organism ; dogs are comparatively immune. 



From this brief review of the peculiarities of the pneu- 

 mococcus it must be obvious that its reputation in pneu- 

 monia depends more upon the regularity with which it is 

 found in that disease than upon its capacity to produce a 

 similar affection in the lower animals. 



As in numerous other diseases, we are unable to furnish 

 an absolute proof of specificity according to the postu- 

 lates of Koch. 



The disease is peculiar in that recovery from it is fol- 

 lowed either by no immunity or by one of such brief dura- 



