CHEMICAL CONSTITUENTS 251 



taining both intact cells and the soluble products of cell disintegration 

 yields on immunization not only type-specific antibodies but antibodies 

 reacting with the protein substance which is common to all pneumo- 

 cocci. While the former generally predominate it is the presence of this 

 protein antibody with its broader zone of activity which is responsible 

 for the confusing cross-immunity reactions occasionally encountered in 

 supposedly type-specific sera and which has in some instances led work- 

 ers to deny the existence of three distinct antigenic types of pneumo- 

 cocci. That the two sets of antibodies involved are separate and distinct 

 is shown by absorption tests ; the antiprotein reaction bodies in such 

 sera can be removed by absorption with the protein of a heterologous 

 type without diminishing the titer of specific agglutinins for the homolo- 

 gous culture or the precipitins for the specific polysaccharide of the 

 corresponding type. . . . 



While it had been generally assumed that only the proteins and their 

 derivatives provided the innumerable opportunities for isomerism and 

 subtle changes requisite for the substances exhibiting the phenomena of 

 specificity, the discovery of carbohydrates with specific properties is not 

 so surprising as might appear on first thought. When one considers the 

 number of asymmetric carbon atoms in the hexoses and pentoses, the 

 different points of attachment of the lactone bridge, the possibility of 

 a and (3-glucosidic unions at various positions in the molecule, and the 

 addition of sugar acids, the analogs of amino acids, to the large number 

 of sugars theoretically capable of entering into the composition of such 

 polysaccharides, it becomes clear that perhaps only among the carbo- 

 hydrates could another sufficiently large and protean group of sub- 

 stances be found to afford the possibility of specific manifestations. 



The evidence of the lack of immunizing properties on the part of 

 these specific carbohydrates shown in the table on page 250 was 

 largely supplied by the experiments of Avery and Morgan. 54 Their 

 attempts to immunize rabbits by subcutaneous and intravenous in- 

 jections of the protein-free polysaccharides of pneumococci in con- 

 siderable amounts and in repeated doses invariably failed to stimu- 

 late the production of any demonstrable antibodies in the serum 

 of rabbits so treated. The isolated protein, on the contrary, was 

 antigenic, but the antibodies it induced reacted with the nucleo- 

 protein fraction of both homologous and heterologous types. In 



