VEGETABLE POISONS 95 



tories into essences nutritive and beneficial to some 

 organisms, neutral or hurtful to others. How very 

 little we know of the process, still less of the 

 reason for the effects of the various products ! 



Take the common stinging nettle, referred to 

 above as the favourite food of so many caterpillars. 

 The stinging mechanism has been explained to us as 

 consisting of hair-like tubes, sharply pointed, each 

 with a bulbous reservoir at its base, filled with an 

 acrid fluid which, in some exotic species, is of deadly 

 potency. We conceal our ignorance of the real 

 nature of this fluid, and of the means of counteract- 

 ing its effects, by explaining to each other that its 

 poisonous principle is neither corrosive, nor gaseous, 

 nor neurotic, but irritant, which leaves the matter 

 much as every village child knows it. 



But how is this poison produced, and why 1 

 Whence is it distilled, and by what unerring pro- 

 cess 1 If it is to protect itself, and not out of sheer 

 cussedness that the nettle stings, what does it seek 

 protection from ? Not, as we have seen, from cater- 

 pillars; and if it is a device to secure immunity 

 from man, it is singularly ill conceived, because, 

 being a plant of some beauty of foliage, its offensive 

 properties only serve to bring upon it persecution, 



