OF NATURAL HISTORY. 9 



culty of contrafting and extending its body, the nature of this be- 

 ing will not be changed ; but we will be unable to determine whe- 

 ther it poflefles any portion of life. This is nearly the condition of 

 the fmall fedions of a polypus, before their heads begin to grow. 

 The wheel-animal, the eels in blighted wheat, and the fnails re- 

 corded in the Philofophical TranfaQions, afford inftances of every 

 appearance of fenfation, or even of irritability, being fufpended, 

 not for months, but for feveial years, and yet the life of thefe ani- 

 mals is not extinguifhed ; for they uniformly revive upon a proper 

 applit:ation of moifture. 



Thefe and fimilar fads fhow, that we are entirely ignorant of the 

 eflence and properties of life. What life really is, feems too fubtlle 

 for our underftanding to conceive, or our fenfes to difcern. If we 

 have no other criterions to diftinguifh life, than motion, fenfation, 

 and irritability, the animals juft mentioned continued for years in a 

 ftate which every man would pronounce to have been perfedly 

 dead. It is poffible, therefore, that life may exift in many bodies 

 which are commonly thought to be as inanimate as ftones. Hence 

 it would be rafh to exclude plants from~ every fpecies of fenfation. 

 The degrees of fenfation decreafe imperceptibly from man to the 

 fea- nettle, gall-infedts, and what are called the moft imperfed ani- 

 mals. Every vegetable, as well as the fenfitive plant, fhrinks when 

 wounded. But, in moft of them, the motion is too flow for our 

 perception. When trees grow near a ditch, the roots which pro- 

 ceed in a diredion that would neceflfarily bring them into the open 

 air, inftead of continuing this noxious progrefs, fink below the level 

 of the ditch, then fhoot acrofs, and regain the foil on the oppofite 

 fide. When a root is uncovered, without expofing it to much heat, 

 and a wet fpunge is placed near it, but in a different diredion from 

 that in which the root is proceeding, in a fhort time the root turns 

 towards the fpunge. In this manner the diredion of roots may be 

 T B> varied 



