i WHAT LIFE IS 3 



matter, while they give no clear indications of the possession 

 of sensation or voluntary 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 pre- 

 sented 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 Encyclopaedia) summed it up in three 

 words " Continuity, Rhythm, and Freedom," true, perhaps, 

 but not explanatory ; while Herbert Spencer declared it to 

 be " the definite combination of heterogeneous changes, 

 both simultaneous and successive, in correspondence with 

 external co-existences and sequences." This is so technical 

 and abstract as to be unintelligible to ordinary readers. 



The following attempt at a tolerably complete definition 

 appears to sum up the main distinctive characters of living 

 things : 



Life is that power which, primarily from air and water 

 and the substances dissolved therein, builds up organised and 

 highly complex structures possessing definite forms and 

 functions : these are preserved in a continuous state of decay 

 and repair by internal circulation of fluids and gases ; they 

 reproduce their like, go through various phases of youth^ 



