PATHOGENICITY FOR EXPERIMENTAL ANIMALS 203 



correspondence in chemical structure to soluble specific substance 

 of Pneumococcus, must have been non-specific, and this surmise is 

 strengthened by the fact that a slight adjuvant action in favoring 

 infectivity was also noted when streptococci instead of pneumo- 

 cocci were the organisms so treated and inoculated. 



The influence of pneumococcal autolysates on the invasiveness 

 of pneumococci injected intradermally into rabbits was studied by 

 Goodner. Whereas autolysates favored the pathogenicity of the 

 culture used, they failed to alter its virulence. The evidence, taken 

 as a whole, favors the hypothesis that the action of culture fil- 

 trates, extracts, autolysates, or specific capsular polysaccharides 

 in increasing the infective power of pneumococci is to interfere 

 with the natural defensive processes of the body and thereby lower 

 the host's resistance rather than to add to the virulence of the cell 

 itself. 



CULTURAL CONDITIONS AND VDIULENCE 



Influences that stimulate the anabolic processes of the pneumo- 

 coccal cell make for virulence. Enrichment of the cultural medium 

 with blood, normal serum, or other growth accessories, the proper 

 concentration of hydrogen ions, and optimal temperature of in- 

 cubation enable the organism to elaborate capsular substance, 

 which, as will be shown in other portions of the present volume, 

 may determine the invasive power of a given strain. Frequent 

 transplantation in favorable media of pneumococcal cultures taken 

 at the period of maximal growth not only maintains but increases 

 virulence (Wadsworth and Kirkbride 1471 ). Repeated transfer by 

 means of the automatic device of Felton and Dougherty 423 of 

 young cultures of a pure-line strain of Type I Pneumococcus into 

 a fresh supply of sterile skimmed milk caused an avirulent strain 

 to acquire a virulence ten million times greater than that of the 

 original culture. Within a wide range, the hydrogen ion concen- 

 tration of the milk appeared to have only a slight effect on viru- 

 lence when transplants were made at two-hour intervals. However, 



