ANTIGENICITY OF PNEUMOCOCCUS 329 



duced intoxication, while the use of acetone and other agents in 

 removing the lipids from the vaccine destroyed its antigenic power. 



In the case of Type III Pneumococcus, Tillett 1400 found that re- 

 peated injections of heat-killed cultures into rabbits were effective 

 in producing active immunity against infection with a virulent 

 strain of the homologous type. Even heterologous strains, de- 

 vitalized by heat, were capable of affording similar protection to 

 Type III cocci. Moreover, this form of active immunity could exist 

 in the absence of demonstrable type-specific antibodies and appar- 

 ently was unrelated to the variety of Pneumococcus used for im- 

 munization. Tillett considered that this anomalous immune state 

 was dependent upon the exaltation of the same factors which af- 

 ford normal rabbits material resistance to some strains of Type 

 III organisms. 



Employing Type II strains, Gaspari, Sugg, Fleming, and 

 Neill 503 learnt that the continued injection of heat-killed cultures 

 of this type led to a decrease in type-specificity and to an increase 

 in the species-specificity of the serum of the treated rabbits. For 

 the preparation of diagnostic serum of high type-specificity the 

 authors preferred as an antigen the heated cells of virulent pneu- 

 mococci administered over a comparatively short immunization pe- 

 riod. A gradual shift from type-specificity to species-specificity is 

 no uncommon occurrence in horses that have been under immuni- 

 zation for long periods of time with either living or dead organisms. 



Day 307 reported that it was generally desirable to kill the cells 

 with heat for the production of antibodies, but warned against the 

 use of a temperature as high as 100° for the purpose, since such a 

 degree of heat destroyed the antigenic properties of the culture. 

 However, this has not been the experience of the authors of the 

 present volume. As might be expected, Day, and also Harley, 592 

 found that any agent which promoted the digestion of the cell, and 

 which consequently led to the breakdown of its constituents, weak- 

 ened or finally abolished the ability to call forth type-specific anti- 



