CONTRIBUTIONS TO THE STUDY OF IMMUNITY. 37 



and complement of the same species. An immune serum inactivated 

 by heating to 56 C. can always be reactivated by the addition of 

 fresh blood serum from an animal belonging to the same species as 

 that from which the immune serum was derived. The complements 

 of other species of animal, however, reactivate this immune body 

 in the most divergent manner. 



The results of the combining experiments were readily harmonized 

 with the requirements of the side-chain theory. The immune body 

 is nothing but a side-chain with two haptophore groups, which has 

 been produced in excess and thrust off into the blood. One of these 

 haptophore groups possesses a strong chemical affinity for the corre- 

 sponding group of the erythrocyte, and ordinarily it serves to anchor 

 nutritive material possessing corresponding haptophore groups to 

 the cells. The other haptophore group is able to combine more 

 or less completely with complement present in the serum. It is 

 probably designed to collect from the blood plasma the ferment- 

 like complement, which, by splitting up the nutritive substances, 

 makes their assimilation possible. 



There is, however, another view to take of these phenomena. It 

 is comprehensible that the cell, as such, produces the two compo- 

 nents necessary for haemolysis simultaneously and in relation with 

 each other, in such fashion that in the assimilation of the substances 

 anchored, it constantly produces the complement required by means 

 of its own activity and does not depend on the supply from with- 

 out, from the blood plasma. The assumption of such a complex 

 system in which two members so intimately connected are yet 

 so readily dissociated offers difficulties which it is unnecessary to 

 discuss further, especially because, as will be seen later, experi- 

 ments have precluded this possibility. 



If, however, the side-chain theory is correct we shall expect: 



1. That immune body and complement are not present in the 

 immune serum in equivalent proportions, but that quantitatively 

 they may be independent of each other. 



2. That the same group of the red blood-cells which in haemolysis 

 combines with the immune body causes the production of the im- 

 mune body. 



3. That cells which possess such form of complex side-chains are 

 enabled by the presence of the complementophile groups to abstract 

 complement from the blood serum. 



1. The question w r hether in the immunity reaction only the inac- 



