378 Chapter XII 



an injection of antitoxin eliminate it from their body much more 

 rapidly than do those which prepare it in their own body; thirdly, 

 that antitoxins are sometimes found in the blood of healthy animals, 

 who have had no attack of the disease nor any injection of the 

 specific toxin. Let us examine these objections more closely, ob- 

 jections all based on well-established facts. 



It has been shown that the antitoxin produced by the animal is 

 sufficient to neutralise a quantity of toxin much greater than that 

 which was injected into the animals supplying the antitoxic serum. 

 [397] Knorr 1 , from his experiments, calculated that a horse reacts to one 

 unit of toxin by the production of 100,000 units of antitoxin. This 

 statement certainly does not allow us to affirm that all the antitoxin 

 corresponds to toxin, but it does not eliminate the possibility that 

 toxin, subjected to the influence of the cells of the animal body, 

 may be found, in a modified form, in the product of these elements. 

 This hypothesis would be quite sufficient to explain the very remark- 

 able specificity of antitoxins. 



If the toxin, in order to be modified by the living cells, must be 

 subjected to some special action on the part of the latter, we can 

 readily understand that this process must demand a greater or less 

 length of time; this would lead to a much slower elimination of 

 the antitoxin than in the case where it had been injected, ready 

 prepared, into a normal animal. From the commencement of his 

 researches on immunity against poisons, Ehrlich 2 distinguishes two 

 kinds of this immunity, an active immunity which is obtained as 

 the result of the introduction of toxins into the animal, and a 

 passive immunity, another form of the refractory condition which is 

 set up by the injection of antitoxic serum formed in the actively 

 immunised animal. Von Behring 3 applies the term isopathic im- 

 munity to active immunity, and to passive immunity that of antitoxic 

 immunity. It is generally admitted that the first kind of immunity 

 is more slowly acquired, but that it persists for a much longer period 

 than the second (passive or antitoxic immunity) which is acquired 

 immediately after the introduction of the antitoxin, but which, on 

 the other hand, lasts for a short time only. This view is supported 

 by numerous observations on the very rapid disappearance of the 



1 Miinchen. med. Wchnschr., 1898, p. 321. 



2 Deutsche med. Wchnschr., Leipzig, 1891, SS. 976, 1218; [Ztschr. f. Hyg., 

 Leipzig, 1892, Bd. xu, S. 183]. 



3 "Allgemeine Therapie der Infectionskrankheiten " in Eulenburg u. Samuel's 

 " Lehrbuch der allgemeine Therapie," Berlin u. Wieii, 1899, Bd. in, S. 997. 



