350 THE. SNAKES OF SOUTH APRICA: 
suddenly disturbed their slumbers, whereupon both simul- 
taneously struck fiercely at the intruder. Both missed their 
aim, and four streams of venom struck one of the plate glass 
sides of the cage and ran down the glass. The venom, when 
ejected, is watery, more so than that of the Cobra. 
In the process of collecting venom by forcing a snake to bite 
over the rubber-covered rim of a watch-glass or wine-glass, the 
fangs are often erected and remain so, but no venom flows until 
the glands are compressed with the fingers. 
It was amply demonstrated in this manner that the erection 
of the fangs did not cause an automatic constriction of the 
masseter muscle fibres. To eject a full charge of venom, the 
snake is obliged to grip and compress its head strongly. The jaws 
of Puff Adders may be extended to their fullest extent yet 
the fangs are not elevated unless the reptile so desires. I have 
frequently distended the jaws of Puff Adders and watched them 
elevate and depress their fangs. The anterior maxillary bones 
to which the fangs are attached are worked independently of any 
other parts of the mechanism of the jaws. 
Taking twelve Puff Adders, I made each in turn bite over the 
thick rim of an ice-cream glass. The instant the rim of the 
glass touched the snake’s nose it bit fiercely, both fangs darting 
up at the proper striking angle, and then descending with great 
violence against the inner side of the glass. Each snake was 
made to bite three or four times. The fangs in each instance 
would strike the glass and slip upwards towards the rim. Not 
even the fraction of a drop of venom was shed by five of the 
snakes. One yielded about three drops, and the rest a very 
small quantity. From the twelve snakes, I collected seven 
drops of venom. I tried this experiment several times and found 
that, although the snake bit the side of the glass freely, either no 
venom, or only a very small quantity was shed. On the con- 
trary, when I covered the top of the ice-cream glass with a 
rather thick piece of sheet rubber, these same Puff Adders in 
biting through it, shed an average of three to five drops and even 
ten drops each, into the glass. 
In the former experiments, I was careful to examine the 
reptiles’ mouths to see if venom by any chance had been shed 
within the mouth, but, with one or two exceptions, there was 
not a trace of venom to be seen. 
