R. J. DUBOS 



enzymes inactivate the specific M protein antigens of group A strepto- 

 cocci (8,13). Contrary to what is observed with lysozyme, however, 

 the polysaccharidases and proteases do not aflfect in any way the 

 viabiHty of the treated cells, even when they rid it entirely by hydrolysis 

 of the specific polysaccharides or proteins. It is likely, therefore, 

 that, instead of being considered as structural constituents of the 

 bacterial bodies, the capsular polysaccharides and the M proteins 

 should be regarded as excretion products which accumulate around 

 the cell, since they can be removed or destroyed without interfering 

 with the essential living processes. 



There are many other instances of biological reactions which, 

 because of the specific relationships they bear to certain cellular com- 

 ponents of bacteria, can be used as indirect methods for the analysis 

 of cellular structures. Let us mention, for example, the remarkable 

 selectivity of pure lines of bacteriophage with reference to the strains 

 of bacteria which they can attack. The relationship between speci- 

 ficity and cellular structure is illustrated by the fact that the bacterio- 

 phage can be absorbed specifically by the cells, living or dead, of the 

 susceptible bacterial cultures. It has also been found that, in certain 

 cases, soluble fractions extracted from the susceptible bacterial cells 

 inhibit specifically the lysis of the homologous organisms by the bac- 

 teriophage. It is likely, therefore, that the phenomena of bacterio- 

 phage lysis will also yield a number of new specific reactions which 

 by revealing the existence and nature of new types of receptors could 

 serve in the analysis of cellular structure. 



The biological phenomena which we have considered have in 

 common the following characteristics permitting their utilization as 

 indirect cytological methods. They are all the result of a reaction 

 between a given reagent (antiseptic, enzyme, antibody, bacterio- 

 phage) and a specific cellular receptor, this reaction manifesting itself 

 by inhibition of growth, enzymic destruction of cellular component, 

 agglutination or lysis by antibody, or lysis by bacteriophage. In 

 many cases the reagent can be absorbed on the homologous cell sub- 

 strate, and the reaction can be inhibited by the addition to the system 

 of the specific substrate which constitutes the cellular receptor. In- 

 hibition of growth, enzymic decomposition, agglutination, lysis, etc,, 

 are only the secondary manifestations of primary reactions which de- 

 pend upon the union between the cellular receptors, on the one hand, 



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