6 SCIENCE PROGRESS. 



Metschnikoff and his pupils. The antitoxin serum acts 

 antagonistically against the toxin in corpore or in vitro on 

 lines and principles determined by quantity ; so that the whole 

 theory of mechanical phagocytosis of Metschnikoff has be- 

 come superfluous as far as acquired immunity is concerned. 

 When an animal is rendered immune either by repeated 

 injections of attenuated culture or by small (non-fatal) doses 

 of toxin the result is always the same ; viz., the appearance 

 in the blood of chemical substances (antitoxin) ; such a 

 condition of the blood or blood serum becomes established 

 and can be further used both protectively and curatively 

 without any phagocytic interference. In the case of acquired 

 immunity produced by toxin injection, the action of 

 phagocytes, that is, of cells swallowing bacteria, is a fortiori 

 out of place, because no bacteria at all are introduced ; the 

 curative action of antitoxin serum in tetanus and diphtheria 

 deals with the neutralisation of toxin that had been formed 

 and is circulating in the tissues of the infected body, and 

 therefore also in this the swallowing up and destroying of 

 bacteria has no place. 



The manner in which in acquired immunity the antitoxic 

 condition of the blood is brought about is not known. 

 There exist theories only on this subject ; thus Buchner 

 inclines to the view that the toxins themselves, produced 

 by the specific bacteria in the infected body, become by the 

 action of the tissues converted into antitoxins ; whereas 

 Behring and also Roux ascribe the production of antitoxin 

 to the tissues themselves, these latter being stimulated by 

 the toxins and thus produce or secrete the latter as a sort 

 of self-defence. As a matter of fact in the production of 

 diphtheria antitoxin of gradually-increasing potency in the 

 horse (Roux), this latter has to be injected with gradually 

 increasing quantities of pure toxin in order to produce 

 further reaction in the animal : tumour and rise of tem- 

 perature. This clearly points to a stimulation of the 

 tissues in the production of the antitoxin. 



All who have worked on this subject agree with 

 Behring that the higher the degree of immunisation in 

 diphtheria, that is, the greater the number of injections and 

 the greater the amount injected, the higher the potency of 



