p 



Natural immunity against toxins 329 



must take place slowly and with great difficulty as is shown by our 

 want of success with tetanus toxin. 



Insects are, as a rule, very tolerant of this latter poison. As, 

 however, the tetanus toxin (we shall illustrate this later) only acts 

 well and in small doses at a high temperature (about 30° C.) and as 

 most insects do not readily adapt themselves to this temperature, 

 it was necessary to choose species capable of living at these high 

 ^temperatures and for this line of study the larva of Oryctes is most 

 suited. It flourishes well at a temperature of 30° — 36° C, and under 

 these conditions exhibits a much greater resistance to infection by 

 Isaria than at low^er temperatures. It can be kept in the incubator 

 for months if placed in glass jars filled with earth mixed with tanner's 

 bark. The injection of enormous quantities of very active tetanus 

 toxin directly into the blood has not the slightest effect on these 

 larvae. Whilst, however, the blood fluid of the Arachnida rapidly 

 gets rid of the poison, that of Oryctes retains it for a very long period. 

 If a small quantity of blood be taken from larvae several months 

 after injection and then injected into mice, these animals contract 

 typical tetanus and quickly succumb. 



The toxin, however, finally disappears from the blood though a 

 certain portion of it may still be found in the pericardial cells and 

 especially in the fat-bodies. 



Never, under any circumstances, was I able to observe that the 

 blood of the larvae of Oryctes exerted any antitoxic action. At the 

 stage when this fluid no longer gives tetanus to mice, it is absolutely 

 incapable of preventing intoxication when mixed, before injection, 

 with tetanus toxin. 



Amongst adult insects the cricket is best adapted for researches 

 on tetanus. The field cricket will bear a temperature even higher 

 than 30° C. It is completely resistant to injections of tetanus toxin, 

 but it showed no more capacity than did the larvae of Oryctes or the 

 Arachnida of producing any tetanus antitoxin. 



All the Invertebrata that I have been able to study have exhibited 

 a remarkable resistance against the known bacterial toxins, but the [346] 

 mechanism of this natural immunity could not be exactly made out 

 owing to the difficulty met with in investigating the toxins in the 

 organs and following their modifications. The idea of making use of 

 these lower animals for the purpose of solving the problem of the 

 origin of antitoxins is not realisable, from the fact that the Inverte- 

 brata that have been studied have never, in my experience, produced 



