ENZYMES. 67 



tralization is brought about by some sort of a combination between the 

 toxin and the anti-body. The views are very contradictory in regard 

 to the nature of this combination and the manner in which it is formed. 



The oldest theory, which has contributed much to our knowledge 

 of these conditions, is that of P. EHRLICH, whom we must thank for the 

 method of measuring the quantity of toxin by injection into an ani- 

 mal. The quantity of toxin which is just sufficient to kill a guinea-pig 

 of given weight in a certain time is selected as the unit. According to 

 the so-called side-chain theory of EHRLICH 1 the toxins firstly have a so- 

 called haptophore group, by means of which the toxin can attach itself 

 to a certain cell, and secondly, a so-called toxophore group, by which 

 the toxin exerts its poisonous action. The formation of anti-body 

 after the injection of the toxins EHRLICH explains by the fact that those 

 cells which are attacked by the toxins are supplied with so-called recep- 

 tors, which just fit the haptophore group of the toxins; the toxins are 

 thus anchored on the questionable cells and can then begin their action 

 by aid of the toxophore group. By the attachment of the receptors, the 

 cells are induced to produce new receptors, and indeed, so many recep- 

 tors are produced that they are thrown off and appear free in the blood 

 plasma. The receptors circulating in the blood are the anti-bodies. 

 As these are able to combine with the toxins they can protect against 

 the toxin those cells which are supplied with the same receptor under 

 whose influence they were found. The toxophore group of the toxins 

 can gradually be destroyed on keeping. A toxin so changed can be 

 continuously anchored to cell-receptors and in this way form anti-bodies, 

 but cannot produce any poisonous action. A toxin without toxophore 

 groups is called a toxoid by EHRLICH. It follows that the toxoids can 

 combine with the anti-bodies. 



According to EHRLICH, on the neutralization of a toxin a chemical 

 combination takes place between the toxin and the anti-body, and so 

 much of this combination is formed that either the toxin or the anti- 

 body is completely consumed. Now the bacterial poisons are not 

 simple bodies, but mixtures of several poisons of different toxicity and 

 different avidity toward the anti-bodies. Generally the most poison- 

 ous is first neutralized, but it also occurs that a less poisonous or indeed 

 a non-poisonous body is first combined with the anti-body (proto-toxoids) 

 or that non-poisonous bodies are combined parallel with the true toxins 

 (syntoxoids) . The less poisonous or non-toxic bodies first combined 

 after the binding of the true toxins are called toxons (also epitoxoids). 

 According to the relative quantity and the avidity of the different con- 

 stituents of the toxic solution, the addition of a certain quantity of anti- 

 body can produce entirely different results. 



1 See Michaelis, Die Bindungsgesetze von Toxin und Antitoxin, Berlin, 1905. 



