POISONOUS PLANTS AND ANIMALS 107 



and some warm-blooded quadrupeds, like the skunk, is 

 often poisonous, and is introduced into the wound inflicted 

 by a bite. The elaboration of a sac of the mouth- 

 surface secreting a special quantity of poison to be 

 injected by aid of a grooved tooth, such as we find in 

 poisonous snakes, is only a mechanjcal improvement of 

 this more general condition. The same general poison- 

 ous quality is found in the slime of the skins of fishes 

 which have spines by means of which poisonous wounds 

 are inflicted (sting-rays). And here, too, an elaboration 

 is effected in some fishes in which a sac is provided for 

 the accumulation of the poison, and a specially grooved 

 spine, to convey the poison into the wound inflicted by 

 it. A common fish on our coasts, the weever (probably 

 the same word as viper), is provided with grooved, sting- 

 ing spines, but no special poison-sac. Some of the 

 poison-carrying spines support the front portion of the 

 dorsal fin, which is of a deep black colour, a striking 

 instance of the warning coloration which poisonous 

 animals often possess. 



The poison introduced into wounds by the spines or 

 fangs of animals is essentially similar to that of nettle 

 hairs ; it has the effect of paralysing and of producing 

 convulsions. It is a remarkable fact that formic acid 

 often in insects accompanies the paralysing poison 

 as it does in the nettle and produces intense pain 

 and irritation, which the more dangerous nerve-poison 

 does not. Immunity to a given wound-poison may be 

 produced by the injection of doses of it, at first exces- 

 sively minute, but gradually increased in quantity. A 

 remedial " anti-toxin " is thus prepared from the blood of 

 immunised animals, which is used as a cure or as a pro- 

 tection by injecting it into other animals exposed to bites 

 or wounds conveying the particular poison by the use of 

 which the anti-toxin was produced. Bee-keepers who have 



