HOST RESPONSE TO ANTIGENIC ACTION 435 



whole blood and, furthermore, that the reaction was dependent 

 upon the presence of leucocytes. 



Analogous differences in resistance were observed by Robertson 

 and Cornwell (1930). 1143 In a study of the pneumococcidal action 

 of normal human serum-leucocyte mixtures for freshly isolated 

 strains of pathogenic pneumococci, the authors ascertained that 

 human beings as a group possess in their blood well-marked de- 

 structive properties for all types of Pneumococcus studied. Indi- 

 viduals, however, exhibit wide variations in reaction against differ- 

 ent types, ranging from strong killing effect for organisms of one 

 type to no action or slight effect against strains of another type. 

 In the light of the results of previous experiments in which actual 

 resistance of animals to pneumococcal infection was determined, 

 Robertson and Cornwell interpreted the findings as meaning that 

 human beings in general possess a considerable degree of natural 

 immunity to all types of Pneumococcus, but that some individuals 

 may be susceptible to one or more types and at the same time be 

 resistant to other types. 



By a method employing whole blood, Ward 1480 found that the 

 phagocytic titer against the first three types of pneumococci va- 

 ried through a wide range in different normal human subjects. 

 Similar results were obtained in the same year by Sutliff and 

 Rhoades, 1363 " 4 who measured the pneumococcidal power of normal 

 human blood by a modification of the method of Robertson and his 

 co-workers. Whole blood, to which heparin was added in small 

 amounts as an anticoagulant, was mixed with pneumococci and ro- 

 tated in an apparatus devised by the authors. Parallel determina- 

 tions of the protective power of the samples were carried out. The 

 blood of seventeen out of twenty-seven hospital patients who had 

 not had lobar pneumonia killed from one hundred to ten thousand 

 virulent Type I pneumococci. When mouse-protective power and 

 pneumococcidal power were compared, it was found that six sub- 

 jects possessed both properties and that the serum of ten indi- 

 viduals was bactericidal but not protective, while the serum of 



