SNAKES AND FROGS 191 



line, it could do no more than merely apply itself to the 

 toad's side, and eventually had to give up the attempt 

 to swallow such an unmanageable victim ! I got the toad 

 out, and save for a few scratches made by the snake's 

 teeth it was none the worse, and, having deflated itself, 

 crawled away quite calmly as if this were no unusual 

 experience ! 



It was interesting to see the toad actually save its life 

 by its power of increasing its size, and one wonders why 

 the snake had not caught hold of a limb. Had the snake 

 been a poisonous species, the prey would have been killed 

 by contact with the fangs, and even had it been able 

 first to inflate itself, its subsequent death would have 

 ensured its return to normal size. 



This brings up a point which had always been a difficulty 

 to me until I meditated over this and other observations. 

 If the poison has been evolved by slow degrees from the 

 ordinary non-poisonous saliva, how could this have been 

 brought about ? What use could slightly venomous 

 saliva be to a snake ? For a creature thus bitten might 

 still be able to go away a long distance and die later, 

 where the snake would not find it. A clue was given me 

 during active service in German East Africa, where I 

 first met with the handsome snake called " Boomslang " 

 by the Boers, and was discussing the debated question 

 whether or no it is poisonous. One old Boer told me he 

 had seen one bite a man's arm, which afterwards swelled 

 up dreadfully, although the effects were not serious ; but 

 many Boers said it was not poisonous. This snake is 

 an " Opisthoglyph," i.e. it has not the long fangs of a 

 viperine snake, but some of the back teeth are grooved 

 in part of their length, and a fold of mucous membrane 

 forms a pouch round the groove to conduct the slightly 

 poisonous saliva while the snake mouths its prey, for it 

 does not strike and let go. Now it is easy to see what an 

 advantage it would be to a snake if, whilst it was hold- 



