WHAT LIFE IS 3 



The differences between plants and animals are, however, 

 equally prominent and fundamental. The former are, with 

 few exceptions, permanently attached to the soil ; they absorb 

 nourishment in the liquid or gaseous state only, and their tissues 

 are almost wholly built up from inorganic matter, while they 

 give no clear indications of the possession of sensation or vol- 

 untary motion. But notwithstanding these marked differences, 

 both animals and plants are at once distinguished from all the 

 other forms of matter that constitute the earth on which they 

 live, by the crowning fact that they are alive; that they grow 

 from minute germs into highly organised structures; that the 

 functions of their several organs are definite and highly varied, 

 and such as no dead matter does or can perform ; that they are 

 in a state of constant internal flux, assimilating new material 

 and throwing off that which has been used or is hurtful, so as 

 to preserve an identity of form and structure amid constant 

 change. This continuous rebuilding of an ever-changing highly 

 complex structure, so as to preserve identity of type and at 

 the same time a continuous individuality of each of many 

 myriads of examples of that type, is a characteristic found 

 nowhere in the inorganic world. 



So marvellous and so varied are the phenomena presented 

 by living things, so completely do their powers transcend those 

 of all other forms of matter subjected to mechanical, physical, 

 or chemical laws, that biologists have vainly endeavoured to 

 find out what is at the bottom of their strange manifestations, 

 and to give precise definitions, in terms of physical science, of 

 what "life'' really is. One authority (in Chambers's Ency- 

 clopaedia) summed it up in three w^ords — "Continuity, 

 Ehythm, and Freedom," — true, perhaps, but not explanatory ; 

 while Herbert Spencer declared it to be — " the definite com- 

 bination of heterogeneous changes, both simultaneous and suc- 

 cessive, in correspondence with external co-existences and 

 sequences." This is so technical and abstract as to be unin- 

 telligible to ordinary readers. 



The following attempt at a tolerably complete definition 



