THE PLASTICITY OF LIFE 197 



ing ; it is always being un-made and re-made. We need 

 not believe the rough guess of the old physiologists, who 

 said that we were made all over again every seven years ; 

 but there is no doubt as to the ceaseless changes of break- 

 ing-down and building-up. In spite of all, however, the 

 body does in great measure retain its integrity. The 

 scrap of iron on the window-sill changes : it rusts ; it becomes 

 something else oxide of iron. But the changes in the 

 living body are for prolonged periods not incompatible 

 with a certain permanence of character ; the body retains 

 its integrity. Chemically regarded, life is in great part a > 

 series of combustions ; but we may say of the organism, 

 "nee tamen consumebatur." There is a quality of per- 

 sistent sameness. 



This important idea has been well expressed by Huxley 

 in his Crayfish, p. 84 : 



" To put the matter in its most general shape, the body 

 of the crayfish is a sort of focus to which certain material 

 particles converge, in which they move for a time, and 

 from which they are afterwards expelled in new com- 

 binations. The parallel between a whirlpool in a stream 

 and a living being, which has been often drawn, is as just 

 as it is striking. The whirlpool is permanent, but the 

 particles of water which constitute it are incessantly 

 changing. Those which enter it, on the one side, are 

 whirled around and temporarily constitute a part of its 

 individuality ; and as they leave it on the other side, 

 their places are made good by newcomers. 



" Those who have seen the wonderful whirlpool, three 

 miles below the Falls of Niagara, will not have forgotten 

 the heaped-up wave which tumbles and tosses, a very 

 embodiment of restless energy, where the swift stream 

 hurrying from the Falls is compelled to make a sudden 

 turn towards Lake Ontario. However changeful in the 



