Il8 FORMS OF IMMUNITY TO TOXINS 



get a vicious circle. The poison injures the liver or other organ 

 and impairs its defensive powers. More poison is allowed to 

 circulate in the blood, and the liver is injured still more. When 

 this occurs we are thrown back on the specific methods of dealing 

 with the toxins, which take longer to come into action, and which 

 may be regarded as the second line of defence. In one case, 

 however, we must regard them as of chief importance. Thus in 

 tetanus the toxin is produced locally, and ascends the nerve- 

 trunks without entering the blood-stream or being carried to the 

 liver or leucocytic organs. Here, then, in all probability, specific 

 methods have to be resorted to, and the chance of recovery depends 

 on their early development. 



The question of specific immunity to toxins, and of recovery 

 from intoxication with true toxins, may be considered under three 

 heads : 



1. Acquired immunity, due to disease or to vaccination with 

 toxins or toxoids (chemical vaccination). 



2. Antitoxic or passive immunity, due to the injection of anti- 

 toxic serum, or possibly to its natural occurrence in the blood. 



3. Natural immunity, not due to vaccination, and not accom- 

 panied by antitoxin in the blood. 



It will be convenient to consider them in this order. 



Natural recovery from toxic diseases such as diphtheria and 

 tetanus is not necessarily accompanied by the appearance of anti- 

 toxin in the blood at least, not in demonstrable amounts. Further, 

 it appears from the researches of Abel that antitoxin, when it is 

 formed at all, does not make its appearance until about the eighth 

 day of the disease, at which period the severity of the toxic 

 symptoms may have already begun to decline. What may be 

 called the simple antitoxic theory cannot be maintained. Under 

 natural conditions the process of recovery is not due simply to the 

 production of antitoxin, though it is possible that this comes into 

 action in prolonged cases. 



Further, acquired immunity to toxins is not due solely to the 

 presence of antitoxin in the blood. If it were so it should develop 

 proportionately to the development of antitoxin, and the two should 

 persist for the same length of time, and disappear together. This, 

 however, is not the case. We have already seen that animals in 

 the early stage of immunization to diphtheria and tetanus frequently 

 present a decreased amount of resistance, or hypersensitiveness, 

 to these substances, and may die with symptoms of acute intoxica- 



