70
Scientific Memoirs by
Neither does the mere possession of an active poison-apparatus secure
immunity. For, as we have seen, cobra-venom
proved rapidly fatal to the tree-vipers experimented
upon. 1 And t heD i p s a d œ ,
w h i c h p o s s e s s g r o o v e d f a n g s , a n d t h u s p r e s u m a b l y
related to the venomous snakes, were found 2 to be much more susceptible to
venom than the relatively much smaller and wholly innocent Simotes.3
In what manner, then, is the immunity to be explained?
In answer to this I have at present only an hypothesis to offer: From
what has gone before, it would appear that the
venomous snake does not secure its immunity
through any peculiarity in general structure or physiology per se;n o r , d o e s t h e
mere possession of an active-poison apparatus render the snake immune to the
venom of a more highly virulent species. The one striking feature, which is
uniformly associated with the immunity, is the possession of a venom of a
degree of virulence and other qualities special to the particular species; 4 and
we have seen that snakes are habitually swallowing some of their own venom,
and absorbing small quantities through wounds and abrasions within the buccal
cavity. Under these circumstances, is it not possible that the immunity may
be an acquired condition—a toleration to the venom established through fre
- q u e n t i m b i b i t i o n o f s m a l l q u a n t i t i e s o f t h e v e n o m i n t h e m o d i f i e d o r a t t e n u a t e d
form which the venom assumes when mixed with salivary and gastric juices,
and absorbed through the alimentary canal?5
1 I m p l y i n g t h a t t h e r e a r e d e g r e e s o f i m m u n i t y .
2 V i d e
E x p e r i m e n t s
2 9 ,
3 0 , a n d 3 2 .
3 V i d e
E x p e r i m e n t s 2 6 , 2 8 , a n d 3 1 .
4 R e g a r d i n g t h e p r o b a b l e i n t e r - i m m u n i t y o f t h e C o b r a a n dD
a b o i a , v i d e
p p . 6 3 a n d 7 2 .
5 MITCHELL and REICHERT, l o c . c i t . ,
p . 4 4 , r e v i e w i n g t h e p u b l i s h e d o b s e r v a t i o n s u p o n t h e a b s o r p t i o n o f
venom by mucous surfaces, state that "the verdict of all observers in connection with the venom of the
crotaliæ is that uninjured mucous surfaces, except in the lungs, cannot absorb venom, at least in sufficient
quantities to produce death. In experiments with the venom of the cobra other investigators have gotten
results which are directly contrary; but in our own researches (details of which are given) a large proportion
of the animals survived." And experiments are given to show that "the gastric juices . . . are de-
structive of venoms."
On the digestion of cobra-venom I have the two following experiments :
—
EXPERIMENT LII.—O f a s o l u t i o n o f c o b r a - v e n o m , o f w h i c h 8 m i n i m s k i l l e d a c h i c k e n w e i g h i n g 1 4 o u n c e s
in 14 minutes, 15 minims were taken, and to this were added 15 minims of a freshly prepared and faintly
acid solution of Pepsine (10 grs. to oz. of water) of ascertained activity; and the mixture was digested for
20 hour s at a t emper at ur e r angi ng bet ween 83° t o 90° Fah. The sol ut i on was t hen f i l t er ed, and t he whol e of
the filtrate injected hypodermically into thigh of a chicken weighing 16 ozs. The chicken died in 70 minutes
with all the symptoms of cobra-poisoning.
EXPERIMENT LIII.—Of the same solution of cobra-venom as was used in above experiment 10 minims
were added to 20 minims of a freshly-prepared and faintly acid solution of P a p a i n e
( 1 0 g r s . t o o z . o f
water) of ascertained activity; and the mixture digested for 21 hours at a temperature ranging between 83°t
o 90° Fah. The solution was then filtered, and the whole of the filtrate injected hypodermically into thigh of
a chicken weighing 14 ozs. The chicken died in 58 minutes with symptoms of cobra-poisoning.
These experiments would tend to show that digestion modifies the virulence of cobra-venom: thus,
of a solution of venom of which 8 minims killed a chicken weighing 14 ozs. in 14 minutes, 15 minims
(a slight loss would occur through filtration) when digested with pepsine failed to kill a chicken weighing
16 ozs. until 70 minutes; and 10 minims when digested with papaine failed to kill a chicken weighing
14 ozs. until 58 minutes.
Fact of possessing a poison-
apparatus.
Hypothesis offered in explana
-tion of immunity.