526 BIOLOGY OF PNEUMOCOCCUS 



the virulence and the amount of capsular development." The state- 

 ment of Dochez and Avery just cited should not be construed as 

 meaning that the virulence of a strain of Pneumococcus militates 

 against its ability to provoke the elaboration of immune sub- 

 stances in the animal body. There are other considerations pe- 

 culiar to each pneumococcal type that determine the antigenic 

 properties of its members. The factors may be differences in the 

 chemical constitution of the cellular components or in the manner 

 in which the polysaccharide and other elements of the cell are 

 joined together, which affects the lability or stability of the anti- 

 gen when introduced into the body and, therefore, determines the 

 specific immune response of the animal. Thus, it is known to be 

 more difficult to obtain a potent serum for Type III than for Type 

 II Pneumococcus, and easier to produce serum of higher protective 

 value for Type I than for Type II. Investigations on the twenty- 

 nine separate types formerly in Group IV indicate differences in 

 antigenicity which may follow the principle established by Dochez 

 and Avery. Attempts to produce serum effective against Type III 

 pneumococci, possessing as they do an unusually large amount of 

 capsular material, have been disappointing. 



Filtrates of broth cultures. Much of the early work was done 

 with filtrates of broth cultures or other agents containing the solu- 

 ble, cell-free components of the pneumococcal cell. Of great impor- 

 tance are the investigations by Avery and Morgan (1925), 54 

 Avery and Neill (1925), 59 and Avery and Heidelberger (1925). 49 

 The results of these studies show that solutions or extracts of 

 Pneumococcus containing free somatic protein and free capsular 

 polysaccharide give rise only to species-specific antibodies ; sus- 

 pensions containing mixtures of intact cells and dissociated cellu- 

 lar components induce both species-specific and type-specific anti- 

 bodies ; preparations of intact cells containing no free pneumococ- 

 cal protein stimulate the production of type-specific immunity. 

 Confirmation of these findings came from Barach, 75 Meyer and 

 Sukneff, 898 Ferguson, 436 and from various unreported observations 



