19 233 



this fact corresponds with the observation so frequently made, that "zones of 



inhibited agglutination" are seen to occur far more frequently in the latter than 

 in the former. 



The action of acids upon the bacterial 

 suspensions. 



Malvoz was the first to draw attention to the fact that acids and certain other 

 chemical substances are able to produce the agglutination of bacteria. This agglut- 

 ination by acids cannot be distinguished from that produced by an immune-serum, 

 either macroscopically or by the use of the microscope. Hence there seems to be 

 no just reason for believing that they are due to two différent causes, as Nicolle 

 and Defalle are inclined to do. 



Neither Malvoz nor the investigators who have followed him, Lambotte & 

 BossAERT, Sabrazks & Brengues, Defalle, Weisser & Friedemann, Craw, and others, 

 have given any exact description of the curious course taken by this acid agglut- 

 ination. Our own experiments have been made with B. coli for the most part, 

 which is referred to in all cases where no special notice to the contrary effect is 

 given; a number of experiments were also made with cultures of B. typhosus. 



The results of the experiments once more illustrate the rule that the results 

 obtained with agar-culture suspensions and bouillon-cultures do not agree. The normal 

 saline suspension of B. coli is very easily agglutinated by HCl, while the bouillon- 

 culture is but difficultly so; but an emulsion in bouillon of the bacteria grown 

 upon agar is, again, comparatively readily agglutinated by the acid. 



The most striking characteristic of agglutination by an acid is the irregularity 

 with which it proceeds, as is seen when the acid is added in steadily diminishing 

 quantities to a long series of the test-tubes. 



Strong or complete agglutination is produced by both large and very small 

 amounts of acid, while the intermediate guantities that lie between these two extremes 

 produce little agglutination or euen none at all; this is clearly illustrated by the 

 figures given in Table XIX. This table also exhibits the remarkable variability of 

 the successive subcultures derived from a single stock of B. coli and grown on a 

 single cultivating medium ; the variable agglutinability shewing itself mainly in 

 the agglutination produced by the very small amounts of acid. 



Very important here is the degree of opacity of the bacterial emulsion employed, 

 much more so than it is in the agglutination produced by an immune-serum. This 

 is shewn by the fact that the "zone of inhibited agglutination" occupying the tubes 



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