234 20 



intermediale lielween tliose containing tiie large and tlie very small amounts of 

 acid, when a normal emulsion is used, becomes smaller and smaller and finally dis- 

 appears as stronger and stronger emulsions are employed — that is to saj', emulsions 

 containing more and more bacteria in a given volume; while at the same time the 

 lower limit of agglutination progressively rises, as is shewn by the ligures in 

 Table XX, Series 75, where the experiments were made with orthophosphoric acid. 



The agglutination of B. coli by acids and the manner in which it occurs 

 resemble in many ways the "sedimentation" produced by the interaction of various 

 substances and studied by Neisseh & Friedemann. Thus, when a Va-nornial solution 

 of ferric chloride is added to an aqueous suspension of gum mastic, the latter is 

 precipitated; using varying quantities of the ferric chloride solution, they found that 

 intermediate zones might occur in which this sedimentation did not take place, 

 and that these zones were progressively curtailed as stronger and stronger gum 

 mastic suspensions were employed. This observation exactly agrees with what we 

 have found to be the case in the agglutination of bacteria by acids, which shews 

 that the phenomenon is not peculiar to the last-mentioned class of suspensions, and 

 is of more general occurrence. The experiments of Weisser & Friedemann and of 

 Beckoi.d that are here referred to, contain many more points of interest that will 

 not be further discussed in this paper; it is to be hoped that further researches 

 that are now under way will clear up a number of the questions that suggest them- 

 selves for solution. 



If an ayar-culture of B. coli be heated to from 50° to 100°, it loses much of its 

 power to be agglutinated by an acid; see Tables XXI and XXII, in which the results 

 of the same experiment are tabulated in two different ways for the sake of clear- 

 ness. The figures given in Table XXII record the fact that the agglutination of a 

 suspension heated to 80° may demand 19 times as much orthophosphoric acid as 

 is needed by the same emulsion when unhealed, while that of a suspension kept 

 at 100° for an hour may require 1000 times as much acid as it does before the 

 suspension has been heated at all. It is to be noticed that the first sudden dimin- 

 ution in agglutinability by an acid that is caused by healing occurs between the 

 temperatures of 70° and 80°, just as has been shewn to be the case with the agglut- 

 ination produced by an immune-serum. This circumstance, too, speaks in just the 

 same way against the view that the effect of heating the suspensions is to destroy 

 certain specific substances in the bacteria, corresponding to the immune-bodies in 

 the agglutinating serum; but it affords support to the view held by us, namely 

 that a change takes place in the physical conditions under which the agglutination 

 proceeds, and that the clumping together of the bacteria is impeded. 



Finding that different acids exhibited the power of agglutinating an emulsion 

 of B. coli in very different degrees, we performed experiments with the object of 

 ascertaining whether there was any connection between what is commonly known 

 as the "strength" of an acid (as measured by its power of inverting cane-sugar) and 



