rOLYSACCHARTDES OF MICRO-ORGANISMS 353 



8ume bacteria also produce mixed polysaccharides, the 

 pneumococcus, for instance, giving products containing 

 ghicose and galactose, the tubercle bacillus glucose, 

 arabinose and mannose, and the Vibrios glucose, galactose 

 and arabinose. 



The most important polysaccharides from a bacterio- 

 logical point of view are the so-called " soluble specific 

 substances " which are responsible for the serological 

 behaviour of many organisms. They were first described 

 in the case of the pneumococcus, but since then have been 

 found to occur in a number of other bacteria of several 

 genera. It was shown by Dochez and Avery that filtrates 

 of cultures of pneumococcus contained a substance which 

 gave specific reactions with antisera prepared against 

 the same type of pneumococcus but not with antisera 

 prepared against other types. Later Zinsser and Parker 

 isolated " residual antigens " from alkaline extracts of 

 the organisms ; the residual antigens reacted with the 

 homologous sera, but gav^e no reactions for proteins and 

 were non-antigenic. Dochez and Avery's " soluble 

 specific substance " was heat stable, was precipitated 

 from aqueous solution by acetone or alcohol, was free from 

 protein, and shown to be of a polysaccharide nature. 

 It was accompanied by a nucleoprotein which was common 

 to all the types of pneumococcus, that from any one 

 type reacting with antisera prepared against any of the 

 other types ; it was antigenic and antisera prepared 

 against it gave no reaction with the soluble specific 

 polysaccharides. 



The specific polysaccharides from each type of pneumo- 

 coccus are not only different in their serological behaviour 

 but, also, have been shown to be chemically different, 

 as may be seen from Table 20, where their main properties 

 are summarised. 



