422 BIOLOGY OF PNEUMOCOCCUS 



Mueller and Tomcsik (1924) 938 had described a complex carbohy- 

 drate prepared from yeast that bore certain chemical resemblances 

 to the capsular polysaccharide of Pneumococcus. It remained for 

 Sugg and Neill 1356 to demonstrate that the resemblance extended 

 to the immunological behavior of these two representatives of 

 Schizomycetes and Saccharomycetes. Pneumococci of Type II, but 

 not of Types I or III, were agglutinated by serum from rabbits 

 immunized by injections of a certain variety of yeast, and filtrates 

 of young, unautolyzed broth cultures of the same type of pneumo- 

 cocci invariably precipitated potent antiyeast serum. The anti- 

 yeast serum, furthermore, protected normal mice against Type II 

 pneumococci as well as the average specific antiserum produced in 

 rabbits for this type. The reciprocal reaction of Type II anti- 

 pneumococcic serum with yeast was not so definite, since serum from 

 many normal rabbits was capable of agglutinating yeast. In a 1 to 

 5 dilution, Type II antipneumococcic serum gave clean-cut agglu- 

 tination. The results of absorption experiments with both the anti- 

 yeast (rabbit) serum and the Type II antipneumococcic (horse) 

 serum were the same as those usually obtained in analogous experi- 

 ments with immunologically related, but not identical, species of 

 bacteria. 



The protection against infection with Type II pneumococci con- 

 ferred upon mice by injection of suspensions of heated yeast cells 

 was practically the same as that obtained by vaccination with 

 Type II pneumococci themselves, with the exception that yeast 

 evoked immunity to Type II and not to Type I or Type III or- 

 ganisms. The mutual reactions of yeast and Type II pneumococci 

 were further demonstrated when Sugg and Neill (1931) 1356 em- 

 ployed semi-purified carbohydrate antigens from both yeast cell 

 and pneumococci mixed with homologous antiserums. Antiyeast 

 serum precipitated with, and sensitized guinea pigs to the Type II 

 antigen but was not active with antigens from strains of Type I 

 and III pneumococci. The Type II antigen was almost as reactive 

 against antiyeast serum as against homologous antiserum. Con- 



