200 ON THE MILK-SAP 



poison is prepared, and the excretory duct of this gland 

 runs through the canal in the tooth, and opens at its apex. 

 When the animal bites, the resistance of the bitten body 

 pushes back the tooth, so that it presses upon the gland, 

 which squeezes out of it the deadly fluid, into the wound. 



If we examine, now, the 

 hairs on the leaf of the 

 Nettle, we find a won- 

 derful agreement. The 

 stinging hair consists of 

 a single cell, terminating 

 above in a little knob. 

 Below, it expands into a 

 small sac, which contains 

 the irritating juice. 



The slightest touch 

 breaks off the brittle 

 point with the little 

 knob, the canal of the 

 hair is thus opened, 

 and it penetrates any 

 soft substance; in con- 

 sequence of the pressure 

 which the resistance to its entry exerts upon the sac, a 

 portion of the poisonous juice is ejected out into the 

 wound. The poisons of our native Nettles and Snakes 

 are not of much consequence, but the nearer we approach 

 the tropics the more frequent and more deadly they both 

 become. Where the glowing Indian sun ripens the poison 

 of the fearful Spectacle-snake, there grow the most 

 dangerous Nettles. Every one among us has felt the 

 slight but irritating sting of the Nettle, which it produces 



