INTERREACTIONS OF TOXIN AND ANTITOXIN OQ 



Ehrlich on the one hand and Arrhenius and Madsen on the other 

 agree that the combination of toxin and antitoxin is a chemical 

 union, and takes place in obedience to the laws of multiple 

 proportions : a single molecule of the one substance always com- 

 bines with the same number of the other on complete neutraliza- 

 tion. Bordet denies this, and compares the phenomenon with the 

 absorption of a stain by a colourable substance. His theory is 

 that a molecule of toxin requires many molecules of antitoxin for 

 its complete neutralization, and that it can be partially neutralized 

 or attenuated by a smaller number. Thus he holds that when a 

 small amount of antitoxin is added to a large amount of toxin, 

 there is not a mixture of free toxin and of molecules of toxin- 

 antitoxin (as would occur if either of the theories already discussed 

 was true), but a uniform solution of toxin of diminished potency. 

 Bordet shows that many of the experimental results of other 

 observers are explicable on his theory, and gives some new facts 

 in support thereof. For example, the amount of an emulsion of 

 red blood-corpuscles which can be haemolyzed by the addition of 

 a given quantity of haemolytic serum can be readily determined. 

 We will suppose that i c.c. of the serum just dissolves all the 

 corpuscles in 5 c.c. of the emulsion, and no more. We might 

 suppose that all the red corpuscles have all their combining 

 valencies exactly neutralized, so that we may regard them as an 

 exactly neutralized toxin-antitoxin mixture. This, however, is 

 not the case, for if we add the haemolytic serum in small amounts, 

 say 0-05 c.c. at a time, we shall find that only a small proportion, 

 perhaps 2 c.c., of the same emulsion can be completely haemolyzed. 

 Thus each corpuscle takes up more haemolysin in the second case 

 than in the first. 



The objection may be raised that a red corpuscle is very 

 different from a molecule of toxin. It can undoubtedly combine 

 with a vast number of molecules of its antibody (haemolysin), but 

 it is quite easy to understand how complete haemolysis may take 

 place if only a certain number of its combining valencies are 

 occupied by antibody. But the molecule of toxin is, as we have 

 already seen reason to believe, much smaller than the molecule 

 of antitoxin ; and although this fact does not in itself render it 

 impossible that the toxin is of higher valency than the latter, 

 it certainly renders it unlikely that it is so much higher in this 

 respect that there can be an indefinite number of stages between 

 free toxin and a fully neutralized one. Bordet has, however, 



