GENERAL PROPERTIES AND ACTIONS OF THE VENOM. 79 



The lethal dose of the fresh venom only was tested in cats. We found that 

 a cat weighing 3,000 gm. was killed by the injection of 0.9 c.c. of venom; thus 

 the minimal lethal dose was 0.3 c.c. of venom pro kilogram of the body-weight. 

 This dose is considerably larger than the lethal dose of fresh venom for dogs, 

 guinea-pigs, or rabbits, and slightly larger than the lethal dose for mice. 



Rats were, as stated above, distinctly more resistant to the injection of 

 venom than any of the other animals. A rat weighing 125 gm. was killed by 

 the injection of 5 mg. of dry venom or 0.1 c.c. of fresh venom. Thus the lethal 

 dose pro kilogram of body-weight for rats was 0.8 c.c. of fresh venom and 40 

 mg. of dry venom. 



Cold-blooded verbebrates are distinctly less susceptible to the action of 

 venom than warm-blooded vertebrates. We have tested the lethal effect of 

 venom of frogs, toads, snakes, turtles, eels, heloderma, and fundulus. 



The Heloderma shows a resistance toward its own venom which for pur- 

 poses of protection at least is complete. The injection of 2.25 c.c. of fresh 

 venom — a quantity sufficient to kill 45 guinea-pigs each weighing 500 grams — 

 produces no evident symptoms on the Heloderma, which weighs on the average 

 500 grams. A definite explanation accounting for this marked resistance of 

 the Heloderma to the toxic effect of its venom can not be given at present, but 

 in view of the results of experiments in which the adsorptive power of helo- 

 derma organs for heloderma venom was tested, it appears that the liver, and, 

 to a less degree, the kidney, of the Heloderma exert a specific adsorptive action 

 on the venom and this may explain, in part at least, the resistance of the Helo- 

 derma to its venom.* This resistance on the part of the Heloderma is not due 

 to antibodies in the serum of the Heloderma, since we have found that venom 

 which had been mixed with heloderma serum had not lost any of its toxic 

 power. The relative immunity of poisonous animals against their own venom 

 is evidently a general phenomenon. 



We have found in a single experiment that the immunity of Heloderma 

 toward its own poison does not extend to the snake venoms. The heloderma 

 reacts very quickly toward rattlesnake venom, but, as we had for the deter- 

 mination of this point, only a small supply of snake venom of unknown strength, 

 we can say no more concerning the lethal dose of this venom for helodermas 

 than that it appears not to greatly exceed the lethal dose for rats and guinea- 

 pigs. 



The resistance of the snake to the toxic action of heloderma venom was 

 tested in only two animals, both water-snakes {Utania certalis). One animal 

 which weighed 80 grams died after the injection of 35 mg. of venom, while the 

 other survived the injection of 25 mg. and only died after the second injection 

 of a similar quantity. The lethal dose of venom for snakes appears to be 

 approximately 400 mg. pro kilogram of body-weight. 



The toad (Bufo americanus) shows a marked resistance to the toxic effect 

 of venom. An animal weighing 50 grams was killed by the injection of 15 mg. 

 of dry venom; thus for toads the lethal dose of venom pro kilogram of body- 

 weight would be 300 mg., a quantity far greater than the lethal dose of venom 



*Cf. the chapter on the adsorption of venom, by M, Fleisher and Leo Loeb. 



