Medical Officers of the Army of India.
49
cases, such as that of Experiment LXIII, in which death occurs immediately in
consequence of intravenous injections of minimal lethal doses of venom, evi-
dence of profound blood-change in the form of the characteristic alteration in
colour and absolute incoagulability may be present. But it must be taken into
account that in such experiments the poison enters the blood directly and that
this may have an important modifying effect on the results, for, if the nerve-irri-
tant toxin be more readily absorbed than the septic one, it is evident that under
normal circumstances a lethal amount of the former may have entered the blood
at a time when comparatively little of the latter has been able to do so ; whereas
in cases of direct intravenous injections the full amount of both toxins present in
the dose of venom enter the circulation simultaneously, so that, although death
is almost immediately induced by the action of the nerve-irritant one, the septic
one has been present in sufficient amount to induce considerable blood-change
ere its supervention. Taking every thing into account, then, it appears not to
be improbable that the factor in the venom which acts as a nervous irritant is
incapable of inducing any important changes in the blood, and that the variabi-
lity in the evidence of the occurrence of such changes in different instances is
connected with variations in the amount of the septic factor which has entered
the blood and in the time which has been given to it to produce its maximal
effects there.
The occurrence of seasonal variations in potency is a phenomenon which is
not peculiar to Daboia-venom for we find evidence of it in the case of cobra-
venom also, but the results are more striking in the former case owing to the
fact that, whilst immediately sub-lethal doses of cobra-venom cause profound
intoxication, corresponding doses of normal Daboia-venom do not do so
because the amount of the septic toxin normally associate with sub-lethal
quantities of that which acts as a nervous irritant is too small to occasion any
conspicuous effects. In the case of cobra-venom, samples collected during the
hot and rainy seasons appear, as a rule, to be somewhat less potent than those ob-
tained during the winter, the normal minimal lethal dose of the former for fowls
of about one kilo in weight, amounting to 0.0005 gramme, whilst that of the latter
is 0.00025 gramme. The same holds good in regard to Daboia-venom, the mini-
mal dose capable of occasioning fatal general convulsions in fowls of 1 kilo
i n w e i g h t , a m o u n t i n g t o a b o u t 0 . 0 0 3 g r a m m e i n d r i e d s a m p l e s c o l l e c t e d d u r i n g
the latter part of winter, and rising to about 0.006 or even to 0.0 12 gramme in
those obtained during the course of the hot and rainy seasons. Such variations
in potency appear to occur in the venom of all snakes whether at liberty or in
confinement, but are more uniform and marked in connection with the latter, for
samples of venom of maximal or nearly maximal potency are occasionally ob-
tained from freshly-caught snakes at seasons when those which have been in
confinement for any considerable time are persistently yielding nothing but
G