74 VENOMOUS SNAKES AND THE PHENOMENA OF THEIR VENOMS 



white rats, because in my former experiments (which were not for the purpose 

 of determining the minimum lethal dose) they were easily killed by injecting 

 intraperitoneally the quantities of about o.oi gm. of the dried crotalus venom. 

 Whether the Danish rats belonged to a more resistant stock than the Ameri- 

 can rats, or whether the venom, which was the same collection in both cases, 

 suffered certain elective inactivation during the time of preservation and ex- 

 posure to different climates — in dried state — within a period of less than 

 one year, I can not state. One thing is clear, however — that the toxicity of 

 the same venom was unchanged for guinea-pigs. The estimation of the mini- 

 mum lethal dose for a mouse (Ishizaka) again demonstrates that his species 

 is also more resistant to the action of another crotaline (Lachesis) venom.' 

 The horse is extremely sensitive to cobra venom and also to rattlesnake venom. 

 Monkeys are fairly susceptible to the venom of Cobra and of Daboia, 

 though much more so to the former. With the venom of Cobra the degrees of 

 susceptibility of rabbits and that of monkeys are not very far apart, but such 

 is not the case in regard to their susceptibilities to daboia venom. 



Concerning the minimum lethal dose of snake venom upon man several 

 authors have given their estimates numerically. Thus, the fatal dose of cobra 

 venom for a man of 60 to 70 kilos has been reckoned by Lamb, from the experi- 

 ments upon monkeys, to be 0.015 g^- to 0.0175 g^- Calmette has estimated 

 it to be 0.01 gm., while Fraser puts the figure as high as 0.031 gm. Rogers 

 considers 0.0035 E^- ^^ ^^^ venom of Enhydrina to be surely fatal for a 

 man of 70 kilos. The knowledge of the minimum lethal doses enables us to 

 judge the degree of danger of a given venom. But these numerical indices 

 of toxicity are not sufficient to determine the danger of a given venomous 

 snake. The true viperine snakes — with the exception of certain Asiatic and 

 African species — are least dangerous, because they are small in size and the 

 vepom is comparatively non-fatal. The crotaline snakes are very dangerous, 

 because most of them are large in size, some are arboreal and aggressive, 

 swift and hard to detect, and their venom is peculiarly destructive to tissues. 



The colubrines, especially the elapine snakes, are the most dreaded, 

 because they usually attain large size, are bold and nocturnal, seek their prey 

 in or around the inhabited districts — even invading houses, and their venom 

 is extremely powerful. Finally, the marine snakes are deadly enough, judged 

 from the powerful venom with which they are provided, yet the nature of 

 their habitat is such as to render them apparently less dreadful to the mass 

 of humanity, their victims consisting mainly of fishermen, especially on the 

 coasts of the tropical Pacific and the Indian Ocean. Thus the size of the snake, 

 the frequency of its occurrence near human presence, and its disposition should 

 form the primary factors, and the strength of the venom the secondary factor, 

 in judging the degree of danger of venomous snakes in general. 



1 The statement that the larger the species the less the susceptibility to venom seems to be insuflS- 

 ciently borne out by the experimental data. We are not yet in a position to make such general- 

 ization, because we do not possess enough systematic materials. At present we have to find 

 out the exact data for every species of animal before we say anything about its susceptibility 

 to a given venom. 



