15 229 



D. The effect of heat on the agglutinating serum. 



This question has been attacked by a number of investigators. Thus Jatta 

 found that a serum agglutinating B. typhosus lost none of its power after being 

 kept for 3 hours at 55°. Most authors — Bail, Eisenberg & Volk, and others — 

 have found that B. coli and 1Î. typhosus immune-sera lose a little of their agglut- 

 inating power after being kept for half an hour at 65°, most of it at 70°, and all 

 of it at 75°. The use of sera heated in this way often results in the appearance of 

 "zones of inhibited agglutination", when they are added in regularly diminishing 

 quantities to a long series of test-tubes. In other words, comparatively large 

 amounts of the agglutinating serum fail to produce agglutination, while small 

 quantities of it do agglutinate the bacterial emulsion. 



The descriptions of this phenomenon known to us are qualitative, and do not 

 give exact numerical details of the circumstances under which it occurs, nor do they 

 state whether the inunune-scrum was heated by itself, or in a condition of dilution. 



Our own experiments, detailed in Tables XII to XVIII, Series 53 to 68, were 

 made with three separate B. coli-agglutinating immune-sera derived from a goat. 

 The serum in some cases was heated by itself, in others after dilution with 

 normal saline. 



And here again it must be emphasised that the results obtained differ according 

 as the measurements are made with a suspension of the bacteria yrown on agar, or 

 with a bouillon-culture. The absolute as well as the relative agglutinating values 

 are quite different in the two cases. Further, the results obtained depend very largelg 

 upon the time at which the measurements of the agglutination that has taken place 

 are made, because the velocity of the reaction is often much diminished. 



In consequence of this, we have generally tabulated the results of measure- 

 ments that were taken after various periods of time had elapsed in the several 

 experiments; similarly, the agglutinating powers of the sera were tested on both 

 agar-culture suspensions and bouillon-cultures of the bacteria. In all cases where 

 the experiments were thus duplicated, care was taken to perform the two sets 

 simultaneously, and to make use of the same specimen of the diluted serum, 

 whether heated or not. Thus these experiments are parallel and strictly comparable 

 to one another in every possibly way. 



In agreement with previous workers, we have found tlial temperatures not above 

 60° do not diminish the agglutinating powers of B. coli immune-sera; no "zones of 

 inhibited agglutination" and no other irregularities were observed in the agglutin- 

 ation obtained — see Tables XII and XIII. 



The results were the same whether the serum were heated by itself alone or 

 in a state of dilution. 



