326 Chapter XI 



reasons that the older conceptions on the subject of immunity against 

 poisons were more advanced than were those on immunity against 

 infective diseases. 



Several examples of natural immunity in the lower animals have 

 already been cited. Thus, we have seen in previous chapters that the 

 Infusoria are resistant to poisons that exert a powerful action on a 

 large number of the higher animals, such as the tetanus and diph- 

 theria toxins and especially the ichthyo toxin of eel's serum. We 

 have mentioned the case of the larva of Oryctes nasicornis which is 

 unaffected by large doses of the toxins of certain bacteria and which 

 at the same time is very subject to fatal infections by very small 

 doses of the bacteria that form the poisons. These larvae, like 

 those of the cockchafer, are, however, fairly susceptible to the poison 

 of the scorpion. Several other species of Arthropoda, which 

 have been studied from the point of view of immunity against 

 toxins, have exhibited analogous features. Thus spiders and scor- 

 pions are refractory to tetanus toxin. In one experiment I injected 

 into the abdominal cavity of a Mygale from the Congo (which 

 weighed 7 grm. 5) 1 c.c. of tetanus toxin on two several occasions. 

 This dose is sufficient to kill, with the symptoms of tetanus, 1000 mice 

 of double the weight. The spider, kept in the incubator at 36° C, 

 remained quite well during the two months that the experiment 

 lasted. It exhibited no symptom, not even transient, of muscular 

 stiffening, nor any change in its habits and natural functions. The 

 tetanus toxin disappeared from the blood of the Mygale, but this 

 blood at no time showed the slightest antitoxic power against this 

 poison. This example of natural immunity cannot, therefore, be 

 ascribed to any antitoxic property of the fluids and must be regarded 

 as a case of immunity of the tissues — von Behring's histogenic im- 

 munity. In the present imperfect state of our knowledge it is 

 impossible to describe precisely the mechanism of this immunity. 

 When we say that the spider is refractory to the tetanus toxin 

 because its susceptible elements have no receptors capable of seizing 

 the haptophore group of this poison, we simply give expression to a 

 hypothesis which we are not in a position to verify by experiment. 

 The scorpion, a well-known representative of the Arachnida with 

 [343] segmented abdomen, shares with the Mygale in the immunity against 

 tetanus toxin. The Algerian and Tunisian scorpions {Scorpio afer and 

 Androctonus occitanus) withstand the action of doses of this poison 

 which are fatal for 1000 mice and more. Taking weight as our 



