146 PNEUMONIA 



develops. Pulmonary hepatization has been induced in rabbits by 

 tracheal, intrapleural and intrapulmonary inoculations with less viru- 

 lent cultures. Rats are but little less susceptible than rabbits and 

 mice, then follow guinea-pigs, dogs, cats and sheep. In the less sus- 

 ceptible animals local lesions are more common than in the more 

 highly susceptible. This raises the question of the relative susceptibility 

 of man. It is reasonable to suppose that man is quite refractory, com- 

 pared with rabbits and mice, to the pneumococcus. He generally carries 

 the organism in his mouth, but becomes infected with it only under 

 certain conditions. It does not induce a general septicemia in man. 

 Klemperer has shown that a culture highly virulent to rabbits is fol- 

 lowed by only a local reaction when injected subcutaneously in man. 

 Spontaneous and epidemic pneumonia has been observed in guinea- 

 pigs and the disease has been induced in these animals by inhalation 

 and by intratracheal and intrapulmonary inoculations. The pneumonia 

 thus induced may be either acute or chronic. It often involves several 

 lobes and presents the anatomic characteristics of a catarrhal rather 

 than a croupous process. It is generally fatal. 



The question of the production of a toxin by the pneumococcus has 

 been the basis of much experimental work. The evidence supplied by 

 these experiments seems to show quite conclusively that this organism 

 elaborates or secretes no true toxin like that of the diphtheria bacillus, 

 but like all bacterial proteins it does yield a poison when properly 

 disrupted. When suspended in salt solution the cells easily and quickly 

 undergo autolytic changes whereby a poison is liberated. This has 

 been conclusively demonstrated by the work of Rosenow and others. 



That a certain degree of active immunity to this organism can be 

 established in rabbits and other animals seems to have been demon- 

 strated. For this purpose, heated sputum, heated cultures, cultures 

 attenuated by phenol, cocci dissolved in bile, and the residue left after 

 autolysis have been employed. One attack of the disease in man 

 confers at least no lasting immunity, and often appears to render the 

 individual more susceptible. That the sera of immunized animals 

 have some protection and even some curative value in the disease in 

 both man and animals seems to be demonstrated, but that such sera 

 have true antitoxic values is certainly not demonstrated. Some claim 

 that the sera of immunized animals have a bactericidal action, 



