672 



BACTERIUM 



similarly with Types B and C. The serum contains an antibody that reacts speci- 

 fically with the polysaccharide fraction in the capsule ; and as the polysaccharide 

 varies in the different types, the serum against each type is specific. The poly- 

 saccharide of Types A and B has been isolated, and has been found to flocculate 

 in the presence of a specific serum. If the bacilli are deprived of their capsules, 

 they lose their specificity, and agglutinate equally, though only to a low titre, 

 with sera prepared against any type. 



The nucleo-protein can be separated from the dissolved bacilli by precipitation 

 with acetic acid in the cold. It gives rise to a species antibody, which does not 

 react with the capsulated bacilli or with the polysaccharide, but which agglutinates 

 capsule-free cells of any type, and reacts with the nucleo-protein of any type. 



A serum prepared by injection of smooth, capsulated bacilli contains antibodies 

 to the polysaccharide and the nucleo-protein ; a serum prepared by injection of 

 rough, non-capsulated bacilli contains only one antibody — active against the 

 nucleo-protein. For the classification of the Friedlander group into types it is 

 essential to use smooth bacilli both for the preparation of sera and for agglutinating 

 antigens. Unless this rule is strictly observed, the results will be unsatisfactory. 

 Failure to realize this principle probably accounts for the discrepant results of the 

 earlier workers. 



The capsulated baciUi stimulate the production not only of type-specific 

 agglutinins and precipitins, but also of type-specific protective bodies. Thus 

 a serum prepared by injection of capsulated bacilli of Type A will protect mice 

 against intraperitoneal injection of Type A, but not against injection of bacilli 

 of Types B or C. The nucleo-protein does not stimulate the production of pro- 

 tective bodies ; a serum, therefore, prepared by injection of capsule-free bacilli 

 of any type is unable to protect mice against infection with capsulated bacilli of 

 any type. It is important to note that the polysaccharide in the pure state, 

 though precipitable by immune anti-S serum of the homologous type, is unable 

 to stimiilate the production of immune bodies ; it must be present in combination 

 with the proteins of the cell. The nucleo-protein, on the other hand, is able by 

 itself to stimulate the production of non-specific antibodies. The polysaccharide 

 is present in quite young cultures of Friedlander 's bacillus ; so that filtrates of these 

 cultures may be used as antigens in the precipitin test. 



A few tabular results may make these relations clear. 



TABLE 42 



Anti-smooth Serum acting on Smooth Capsulated Bacilli and on Rough Non-capsu- 

 LATED Bacilli, or on Smooth Bacilli that have been artificially deprived op their 

 Capsules. 



