23 237 



immune-serum and enough acid to produce total agglutination by either of these 

 substances if they were acting upon the emulsion separately' instead of together. 



Very similar conclusions were reached with our stock-culture of B. typhosus. 



The figures obtained in the researches detailed in the preceding paragraphs 

 varied widely from one day to anolher, and were even coulradiclory. Hence it was 

 not possible lo arrive at definite numbers thai would satisfactorily express the pre- 

 cise relations that exist here. For lliis reason we have contented ourselves with 

 the qualitative statements given above. 



F. The action of acids upon the agglutinating 



immune-serum. 



The action of acid upon an agglutinating immune-serum has been subjected 

 to searching investigations at the hands of Pick, Eisenberg & Volk, and others. 

 They have found that an acid can inhibit the specific action of the serum when 

 it is present in sufficienlly large quantities, .but not if ils quantity is small. These 

 facts cannot be doubted, and the change produced in the immune-serum by the 

 acid is probably similar in nature to that produced by the action of heat upon it. 



Eisenberg & Volk, who are followed by later experimenters, explain the 

 phenomena by saying that a portion of the agglutinine is converted into agglut- 

 inoid. But they did not take the precaution in their experiments, so far as one is 

 able to see, of measuring the quantity of free acid present in the various test-tubes 

 from which they drew their experimental results; nor do they state to what extent 

 their bacterial stock could be agglutinated by hydrochloric acid acting alone. 

 Hence it is possible that a portion of the agglutination they describe in the Tables 

 of their results is due to a combination of acid and immune-serum agglutination, 

 or even to acid-agglutination alone. 



Our own researches were made in the following manner. Hydrochloric acid, 

 in various quantities and in exactly-measured degrees of dilution, was allowed to 

 act upon the coli immune-serum, either before or after its dilution, for about 

 2 hours at 37°. The acidified serum was then used for experiment, in some cases 

 directly, in others after careful neutralisation with sodium hydrate solution. Its 

 agglutinating power was measured on both agar-culture suspensions and bouillon- 

 cultures of the bacteria ; as the results given later shew, it is very important that 

 cultures of both kinds should be employed. We examined the effects of both 

 small and large quantities of the acid, allowing it to act upon the serum in 

 strengths varying between V7000 and about ^'4 normal HCl, some of the results 



