UNION OF COMPLEMENT 33 



it is of trifling degree. As a result of numerous experiments, 

 we have come to the conclusion that it is due to variations 

 in the combining affinities of the complement molecules 

 of the serum, as Ehrlich has maintained with regard to the 

 composition of diphtheria toxin. Some of the complement 

 molecules are weaker, both as regards their combining 

 affinities and their haemolytic action, than others ; that is, 

 they correspond to the epitoxoids. This weaker moiety 

 of complement will accordingly be left over in any combining 

 experiment and will thus account for the prolongation 

 of the interval between the first appearance of free comple- 

 ment and the presence of a free haemolytic dose. This 

 supposition will also explain the great variations of the 

 degree to which the phenomenon is observed in the case 

 of different sera ; whereas any explanation seems to be 

 impossible on the supposition that all the complement 

 molecules are the same. Furthermore, the extreme example 

 of a complementoid is got when the serum is heated at 55 C. 

 so as to abolish entirely its haemolytic action, as will be 

 shown below (p. 47). One can still demonstrate in such 

 a heated serum the presence of molecules which retain in 

 part their characteristic combining properties and prevent 

 the' union of complement. The addition of serum heated 

 at 55 C. to fresh serum should increase or lengthen out the 

 phase of incomplete lysis in the added corpuscles, that is, 

 should make the Ehrlich phenomenon more marked, and this 

 is found to be the case. While giving the above as the 

 explanation, we fully recognize that there may be other 

 factors concerned, as the combination of organic molecules 

 like those in question may involve principles which are not 

 yet understood. 



