CONCERNING H^EMOLYSINS. 17 



relative affinity is found in the degree of temperature at which 

 combination occurs. In the case of the lysin obtained by immuniza- 

 tion, which has already been described, the combination of the blood- 

 cells with the corresponding haptophore group of the immune body 

 took place at C. ; the combination of the second haptophore group 

 with the complement took place only at a higher temperature. At 

 C. the fluid would therefore contain immune body and comple- 

 ment in a free state, i.e. uncombined. In this case, of course, it is 

 possible completely to abstract the immune body from this mixture 

 by means of the red blood-cells. This is the most favorable case. 

 Its direct opposite will be one in which the affinity of the two hapto- 

 phore groups is exactly equal. In that case the blood-cells will 

 invariably combine with interbody + addiment in such a manner 

 that equal amounts of the two components are withdrawn from the 

 fluid. Naturally between these two extremes all kinds of inter- 

 mediate phases may exist showing variations in the degree of affinity of 

 these two groups. It seems to us that the most frequent case is 

 that in which the affinity of the haemotropic group of the interbody is 

 not much greater than that of the group fitting the addiment. In 

 this case we are unable to produce free addiment by treating the 

 mixture with erythrocytes; a certain amount of interbody always 

 remains in the serum so that the latter does not completely lose 

 its solvent property. Such sera, which still possess solvent property, 

 cannot, of course, be used for experiments in activation. 



In our investigations on normal sera we met with this last case 

 surprisingly often, and it was this circumstance that made the study 

 of the complements so difficult. We therefore sought to find another 

 method of procedure, one by which these difficulties could be 

 avoided. 



For analytical purposes it is essential, as already stated, to have 

 both components of the serum, viz., interbody and complement, 

 in an isolated form. The interbody can at any time be obtained 

 from the normal active serum by heating, but the production of 

 the complement from the normal serum is not entirely successful 

 because of the above-mentioned difficulties. 



We therefore proceeded on the assumption that every blood 

 serum may contain a whole series of different ferment-like bodies, 

 among which some would be capable of assuming the role of com- 

 plement. It was of course clear that such a combination of circum- 

 stances would only be a fortunate chance occurrence, and that only 



