m, XIII.] LIFE AS ADJUSTMENT. 69 



wliich liis proceedings are conformed to surrounding circum- 

 stances." 



We practically recognize the truth of this definition of 

 life when we attempt to ascertain whether an animal is dead 

 or alive by poking it with a stick. If it responds by motions 

 of its own, we judge it to be alive ; if it merely moves as the 

 stick pushes it, we judge it to be dead. So we decide whether 

 a tree is alive or dead by observing whether the increased 

 supply of solar radiance in spring causes those internal 

 motions which result in the putting forth of leaves. In 

 these cases we recognize the truth "that the alteration 

 wrought by some environing agency on an inanimate object 

 does not tend to induce in it a secondary alteration, that 

 anticipates some secondary alteration in the environment. 

 But in every living body there is a tendency towards 

 secondary alterations of this nature; and it is in their pro- 

 duction that the correspondence consists," 



This formula for vital phenomena is further illustrated 

 and justified by the fact that the degree of life is low or 

 high, according as the correspondence between internal and 

 external relations is simple or complex, limited or extensive, 

 partial or complete, imperfect or perfect. The lowest forms 

 of life respond only to the simpler and more homogeneous 

 changes which affect their total environment. The relations 

 established within a plant answer only to the presence or 

 absence of a certain quantity of light and heat, and to the 

 chemical and hygrometric relations existing in the envelop- 

 ing atmosphere and subjacent soil. In a polyp, besides 

 general relations similar to these, certain more special rela- 

 tions are established in correspondence with the external 

 existence of mechanical irritants ; as when its tentacles 

 contract on being touched. The increase of extension 

 acquired by the correspondences as we ascend the animal 

 scale, may be seen by contrasting the polyp, which can 

 simply distinguish between soluble and insoluble matters, 



