PROPERTIES OF COMPLEMENTS 41 



groups appear to be the same. On the other hand, * anti- 

 complement ' for guinea-pig's complement has very little 

 effect on rabbit's complement therefore the haptophore 

 groups of the two complements appear to be different. We 

 found on investigating the matter that, in the case studied, 

 the combination of complement with sensitized corpuscles was 

 much firmer than its combination with ' anti-complement '. 

 In fact, with the latter there was evidence of some dissocia- 

 tion of complement after combination. We considered that 

 this difference in the firmness of union might explain the 

 difference in the two cases, and said, ' It is quite intelligible 

 that differences shown to exist where the chemical union 

 is of a loose nature may not be detectable when the com- 

 bining affinity is strong.' The facts, however, can be readily 

 explained according to the new views regarding anti-com- 

 plement action. If the anti-serum obtained by injecting 

 guinea-pig's serum is added to fresh guinea-pig's serum, we 

 have all the conditions for deviation of complement, seeing 

 that both the serum receptors and the corresponding anti- 

 substances are present. If, however, we add the anti-serum 

 to rabbit's complement, it is manifest that the specific serum 

 receptors are practically absent ; therefore the complement 

 is not absorbed the anti-complement action is apparently 

 absent. We can, however, add the serum receptors as 

 a minute quantity of heated guinea-pig's serum, and then 

 we find that rabbit's complement is fixed, just as guinea- 

 pig's is ; in other words, the anti-complement becomes 

 effective on other complements when a small quantity of the 

 homologous serum is added to the mixture. This is readily 

 intelligible according to the scheme S + anti-S + C. We have 

 omitted a number of our experiments on this point, as they 

 have not now the significance which we supposed them to 

 have. We may, however, refer to one point which we 

 investigated, namely, as to whether the guinea-pig's com- 

 plement combines with the same molecules in the sensitized 



