CHEMICAL CONSTITUENTS 239 



immunizing properties — it was thought to be the proteins of the 

 cells which performed this function — but now it seems that, in the 

 case of Pneumococcus at least, the protein is merely the vehicle 

 carrying the sugar that decides the immunological character of 

 the saccharide-protein complex of the cell. 



WORK OF EARLIER INVESTIGATORS 



Before discussing the newer discoveries it may be permissible to 

 recount briefly the observations of earlier investigators in order 

 that their bearing on these questions may be borne in mind. The 

 literature before 1923 is notable for its lack of reports of detailed 

 or systematic investigations on the chemistry of Pneumococcus. 

 Here and there one finds communications dealing with a few of the 

 components of the cocci, some fragmentary, some pointing mostly 

 by inference to the existence of proteins, fats, or carbohydrates. 

 The first account was that of Friedlander 487 in 1883. His interest 

 in the peculiar capsular material caused him to carry out a few 

 simple tests to determine its nature. It was soluble in alkali, but 

 insoluble in acetic or mineral acids, in alcohol, ether, or chloro- 

 form, and these properties led Friedlander to believe that the cap- 

 sule was composed of mucin or some related substance. 



While it was a foregone conclusion that the cell contained pro- 

 tein, no direct evidence had been offered proving its existence. The 

 affinity of the cellular material for aniline dyes was presumptive 

 evidence, as was the increase in amino nitrogen during autolysis. 

 The work of Rosenow 1169 and of Avery and Cullen 38 ' 41 proved that 

 intracellular protein must be the source of the smaller nitrogenous 

 molecules arising in the natural self-digestion of the cell. So it was 

 with the fats ; only by their cleavage products were they recog- 

 nized. 



Prior to 1917, none of the constituents of Pneumococcus had 

 been isolated or subjected to chemical study. It was in that year 

 that Dochez and Averv 321 discovered in cell-free filtrates of broth 



