80 



THE VENOM OF HELODERMA. 



pro kilogram for rats, which proved to be the most resistant of the warm- 

 blooded vertebrates tested. The toads showed very profound respiratory dis- 

 turbances and almost complete paralysis for some hours following the injection 

 of venom, but in spite of these alarming symptoms, unless the amount injected 

 was 15 mg. or more, the animals recovered from the injection. 



As is well known, the toad is resistant to a number of poisons besides the 

 one contained in its own skin secretion. Certain of these poisons, notably anti- 

 arin and the poisons of the digitalis group, produce physiological disturbances 

 similar to those produced by toad venom, and it has been suggested that the 

 same mechanism by which the toad is able to protect itself against the latter 

 poison answers also as a protection against the former ones. However that 

 may be, the venom of Heloderma, toward which the toad shows also remarkable 

 resistance, has physiological effects quite different from those produced by 

 antiarin, digitalis, and the toad poisons; consequently, the same explanation 

 will not suffice here. We made no experiments to investigate the nature of 

 this resistance, as our supply of toads was limited. 



Frogs (Rana dimatans and Rana pipiens) proved to be more susceptible to 

 the action of venom than toads. Five frogs weighing between 80 and 85 

 grams died after injection of 4, 5, and 6 mg. of venom; one frog weighing 84 

 grams received 5 mg. of venom and survived; two frogs weighing 80 and 75 

 grams, respectively, survived after injection of 3 mg. of venom; 4 mg. repre- 

 sents, therefore, approximately the lethal dose for a frog weighing 80 grams. 



Tadpoles were found to be more susceptible than adult frogs. Tadpoles 

 weighing approximately 2 grams survived after the injection of 0.025 mg. and 

 died after injection of 0.05 mg. of venom. The lethal dose for a kilo of tad- 

 poles is, therefore, between 12 and 25 mg. of venom, while the lethal dose pro 

 kilogram of frogs is 50 mg. 



Lethal doses of venom for cold-blooded vertebrates. 



Testing the susceptibility of various kinds of turtles to the heloderma 

 venom, we found that all reacted in relatively the same manner to the venom. 

 We used the spotted terrapin and painted terrapin in most experiments, but 

 also used the stink-turtle and mud-turtle. The injection of 5 mg. of venom 

 was found sufficient to cause the death of a turtle weighing 80 grams. The 

 lethal dose of venom for a turtle is, therefore, 65 mg. for every kilogram of 

 body-weight. 



