212 BIOLOGY OF PNEUMOCOCCUS 



power of the organism. Furthermore, there are other and specific 

 factors which may expedite the process. 



DISSOCIATION AND VIRULENCE 



Stryker 1348 in 1916 reported that virulent pneumococci when 

 grown in homologous immune serum fail to form capsules, show a 

 decrease in virulence, and become more susceptible to phagocyto- 

 sis. By passing the altered forms through mice, reversion to the 

 original type takes place. Normal serum has no such effect. The ex- 

 periments of Stryker, therefore, constituted the first demonstra- 

 tion of the ability of the specific antibodies of immune serum to 

 inhibit the elaboration of capsular substance by Pneumococcus 

 and consequently to render the organism vulnerable to the natural 

 defenses of the animal body. Further developments in the investiga- 

 tion of the action of immune serum as well as of cultural conditions 

 on the virulence of pneumococci have already been described in 

 such detail, that, in order to avoid needless repetition, the reader is 

 referred to the chapter on dissociation. 



Summary 



To summarize the data discussed in the present chapter, it may 

 be repeated that in the mouse and the rabbit man has at his dis- 

 posal animals admirably adapted for the several purposes of the 

 bacteriological and immunological study of Pneumococcus. The 

 use of in-bred strains of mice, and presumably of rabbits, reduces 

 the frequency of irregular results in experimental work, especially 

 in quantitative estimations of specific antibodies in immune serum. 

 The monkey, being more closely related in the biological scale to 

 man, presents opportunity for studying the invasiveness of pneu- 

 mococci and their pathological effects in the animal economy. The 

 horse, although obviously unsuited to the study of pathogenicity, 

 by virtue of its size and disposition, serves as the most convenient 

 animal for the production of antipneumococcic serum. Susceptibil- 



