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THE VENOM OF HELODERMA. 



We have, except in one case, compared only the minimal lethal doses of 

 the dissolved dry venom. Although we have investigated the minimal lethal 

 doses of the fresh venom, we have not, as a rule, used the results of these experi- 

 ments in comparing the susceptibility of the various species, mainly on account 

 of the already mentioned marked daily variation in the strength of the fresh 

 venom. It has, however, been necessary in certain cases to compare also the 

 lethal doses of the fresh venom in order to supplement the results as shown by 

 the lethal doses of the dry venom, and in one case (cat) we have tested only the 

 lethal dose of fresh venom. We have noted considerable variations in resist- 

 ance among individuals of the same species, most especially when fresh venom 

 was injected. Dogs showed a considerable individual variation in regard to 

 sensitiveness, and in a lesser degree rabbits and mice showed similar variations. 

 The variability among animals of the same species showed itself always in the 

 direction of a resistance considerable below the average. We did not find indi- 

 viduals showing more than the average resistance. 



We note that among the Avarm-blooded animals tested pigeons are the 

 least resistant. The other animals all show relatively less susceptibility to the 

 lethal effect of venom in approximately the following order: dog, guinea-pig, 

 mouse, rabbit, cat, and rat. The dog, guinea-pig, mouse, and rabbit all seem 

 to have approximately the same degree of resistance to the venom, since the 

 lethal dose of the dry venom is very nearly the same for every kilogram of body- 

 weight of each of these animals. The rat, however, shows distinctly greater 

 resistance to the lethal effect of the venom than any of the other warm-blooded 

 animals. 



Minimal lethal doses of venom for warm-blooded animals. 



It will be noted that the lethal dose of dried venom is approximately the 

 same for every kilogram of body-weight of either dog, guinea-pig, mouse, or 

 rabbit, the lethal dose being approximately 10 mg. for each of these animals. 

 We do not, however, find a similarity regarding the lethal dose of fresh venom 

 for these four classes of animals. The dog appears to be most susceptible to 

 fresh venom; the rabbit, pigeon, guinea-pig, mouse, and rat follow in the order 

 named. It is probable that this apparent variation in susceptibility to fresh 

 venom is due largely to the variation in the toxicity of the venom.* 



*In order to obtain the dry venom, many specimens of fresh venom were mixed; thus the dry venom represents 

 a substance of approximately average toxicity. On account of the great variability in the toxicity of fresh venom not 

 much importance can be attached to the minimal lethal quantities of fresh venom in the case of dogs, in which the 

 number of experiments was necessarily small. 



