IMMUNITY TO TOXINS 123 



(3) altering the nature of the substances on which they are to act. 

 If the term "stimulin" is to be used at all, it should be rigidly 

 restricted to one that acts in the second way, and there is as yet 

 no strict proof that such a body occurs. Substances acting in the 

 third way are called opsonins, and, if the theories of antitoxic 

 action here outlined are correct, antitoxins have this action also. 



Turning now to the process of recovery from bacterial intoxi- 

 cations in natural disease, we find but little evidence that the 

 formation of antitoxin plays any active part in the process. The 

 conditions are not as a rule suitable for the production of this 

 substance, since the constant flow of the toxin into the circulation 

 would lead rather to a summation of negative phases and the pro- 

 duction of hypersensitiveness. Further, the process of recovery 

 may have commenced before antitoxin appears in the blood a 

 phenomenon which, when it occurs, we may regard rather as a 

 means of preventing reinfection than as a mechanism for the cure 

 of the original attack of the disease. (It may be pointed out that 

 in the case of diphtheria the studies of Ruth Tunnicliffe lead us to 

 believe that the process of recovery runs parallel to, and is due 

 to a rise in, the opsonic index, and that the main factor in the cure 

 of the disease is the removal of the bacilli by a process of phago- 

 cytosis, and consequent cessation of the absorption of toxin.) In 

 prolonged diseases it is possible that the production, and especially, 

 perhaps, the local production of antitoxin, may play some part in the 

 process. In other cases, perhaps, the toxin is dealt with by some of 

 the simpler chemical processes considered already and submitted to 

 various changes of oxidation, etc., and thus rendered inert ; but of 

 this we have but little knowledge, the main studies of the methods 

 in which the body deals with toxins having been devoted to the 

 phenomena occurring in highly immunized animals and brought 

 about by their sera. 



Some experiments designed by Wassermann as evidence in 

 support of the side-chain theory may be alluded to in this con- 

 nection. He found that the injection of tetanus toxoids into 

 highly susceptible animals (guinea-pigs) has the power of render- 

 ing them partially immune to tetanus toxin for a short period. 

 Thus, when the toxoid was injected, followed in an hour's time 

 by unaltered toxin, the lethal dose of the latter was greater than 

 in a normal animal. On the other hand, after a day or two the 

 animal became more susceptible, being killed by less than the 

 minimal lethal dose for normal guinea-pigs. This he explained 



