THE BACTERIAL CELL 



lipid-protein-polysaccharide complexes mentioned above. The poly- 

 saccharide components determine the immunochemical specificity of 

 the different species. The protein component, on the contrary, ap- 

 pears to be essentially the same in all the members of the group; in 

 fact, it can be made to combine with the different specific polysac- 

 charides to reconstitute complexes similar to those which normally 

 occur in the cell (16). 



In general, the immunochemist has concerned himself primarily 

 with the constituents which are present at the cell surface becaase 

 these elements appear to play the most important part in the phe- 

 nomena of immunity. However, other proteins, polysaccharides, etc., 

 which certainly occupy less superficial positions in the cell have also 

 been recognized by immunochemical analysis. A striking illustration 

 of the potentialities of immunochemical methods in cytology is given 

 by the case of the typhoid bacillus. Specific antibodies have been 

 prepared for the following cellular components of this organism: tlie 

 flagella; the O and Vi antigens of the cell surface; the R, p, and Q 

 antigens, which are intracellular components. Living typhoid bacilli 

 resuspended in solutions of these different antibodies exhibit a charac- 

 teristic behavior which is determined by the relative position of the 

 corresponding antigen in the cellular architecture. Loss of motility, 

 different patterns of agglutination, bacteriolysis, etc., are phenomena 

 which are characteristic for each antigen-antibody reaction and 

 which can be interpreted in terms of cellular organization of the 

 different antigens. 



Dyes, antiseptics, and antibodies are not the only reagents 

 which can be used to recognize and identify the cellular receptors. 

 If it be found, for example, that a given enzyme attacks the cells of a 

 certain microbial species causing death or the alteration of a character- 

 istic cellular property, it can be surmised that the chemical substrate 

 which is susceptible to the enzyme is present in the cell under con- 

 sideration and that it plays some part in the function altered by the 

 enzyme. Thus, the fact that lysozyme causes the death and lysis of 

 the cells of several bacterial species indicates that the mucopoly- 

 saccharides hydrolyzed by this enzyme are essential components of 

 the cellular structure of the susceptible species (15). It has been shown 

 also that other polysaccharidases decompose the capsular polysac- 

 charides of pneumococci and of streptococci, and that proteolytic 



55 



