CHAPTER VIII. 

 THE SIDE-CHAIN THEORY. 



WHEN it was discovered that the injection of the serum of an 

 animal that had been rendered immune to diphtheria could protect 

 another animal against infection with the corresponding organism, 

 and could even arrest the disease after this had actually developed, 

 the question naturally arose how this remarkable effect could be 

 explained. Different possibilities, of course, suggested themselves. 



Roux and Buchner at first expressed the opinion that the anti- 

 toxin produced its effect by acting upon the cells of the body in such 

 a manner as to increase their resistance, or to diminish their suscep- 

 tibility to the corresponding toxin. In other words, they imagined 

 that the antitoxin called forth a rapid immunization of the cell. 

 This view was abandoned when it could be shown that the addition 

 of antitoxic serum to a toxin outside of the body is capable of pre- 

 venting the effect of the latter, when the mixture is subsequently 

 injected into the body. 



Ehrlich first demonstrated this with the blood of mice which had 

 been immunized against the vegetable toxin ricin. He found that 

 several multiples of the minimal fatal dose of this substance could 

 be injected into animals, without producing any toxic symptoms, if 

 an appropriate amount of blood from a correspondingly immunized 

 animal (antiriciri) had previously been added to the ricin solution. 

 Eraser similarly found that the antitoxin directed against snake 

 poison (antiveniri) acted much more energetically, if it was first 

 mixed with the corresponding toxin (veniri) outside of the body, 

 than when its injection immediately followed or preceded that of 

 the toxin. Analogous experiments with toxic eel serum, crotin, and 

 the hemolytic component of the tetanus toxin (tetanolysiri) led to 

 similar results. 



These observations also rendered untenable the view that the anti- 

 toxin only acquires active properties as the result of a ferment-like 

 transformation of the substance on the part of the body cells. Evi- 

 dently the antitoxin acts directly upon the toxin, and in interpreting 



