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.o1 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 gm. to 0.0175 gm. Calmette has estimated 
it to be o.or gm., while Fraser puts the figure as high as 0.031 gm. Rogers 
considers 0.0035 gm. of the venom of Enhydrina to be surely fatal for a 
man of 7o 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 
venom 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. 

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