104 VARIATIONS IN PATHOGENICITY [CH. vn 



Eyre, Leatham and Washbourne (1906) endeavoured by 

 the method of animal inoculation to ascertain whether the 

 difference in the lesions caused depended upon specific differ- 

 ences in the pathogenicity of the infecting strains. They 

 found that strains of the pneumococcus isolated from cases of 

 lobar pneumonia when inoculated subcutaneously into the 

 guineapig almost invariably gave rise to a local inflammatory 

 exudation of a fibrinous type, whereas strains isolated from 

 cases of broncho-pneumonia, when similarly inoculated, almost 

 invariably gave rise to a local inflammatory exudation of a 

 celMar type, easily distinguished from the other. A number 

 of strains of pneumococci obtained from a " neutral " source, 

 such as the mouth, likewise showed differences in the nature 

 of the inflammatory reaction they provoked at the site of in- 

 oculation, some belonging to the "fibrinous" type and others 

 to the " cellular " type. They further showed that this feature 

 was not associated with any other differences between the 

 strains as regards morphology or cultural characters or fer- 

 menting properties and was quite independent of their degree 

 of virulence. They therefore regarded it as a specific character. 



If the lesions produced in the body during the course of 

 an infective disease are subject to variation, are those which 

 result from the artificial inoculation of animals any more 

 constant? 



The materials from which to form an opinion on this point 

 are somewhat scanty. That the feature in some cases is very 

 constant was shown by Shattock (and others, 1907) by means 

 of the following experiment. They grew a strain of human 

 tubercle bacilli for eight weeks in the spleen of a pigeon. The 

 subsequent inoculation of the organisms into a guineapig gave 

 rise, not as might have been expected to the lesions charac- 

 teristic of avian tubercle, but to those characteristic of the 

 human type. Baldwin (1910) likewise grew the human type 

 of tubercle bacillus for 19 months continuously in the bovine 

 tissues without in any way affecting its pathogenic powers to- 

 wards rabbits and guineapigs. 



On the other hand, we have quoted in an earlier paragraph 

 an instance of a certain strain of the diphtheria bacillus which 



