NUTRITION. 199 



take out some of the most valuable portions of the nutri- 

 ment. Suppose that in a mill, a workman, whose business 

 is to shovel out wastes, becomes crazy, and shovels wheat 

 or flour out of the mill into the stream below. The dis- 

 eased kidney may be said to have become crazy, and in 

 the disease called " diabetes " throws out sugar, and in 

 " albuminuria " excretes albumen. 



Blood Streams like Water Pipes and Sewer Combined. 



It is as though the water supply of a city house was taken 

 from the sewer ; each organ needing a supply of building 

 material acts like a filter, taking from the blood what it 

 needs, paying no attention to the impurities present, and the 

 organs of excretion select the impurities, allowing the useful 

 substances to pass on to the places where' they are needed. 



A Living Eddy. Huxley has very aptly compared the 

 body to an eddy, whose form remains the same, but whose 

 particles are ever changing. 



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

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

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

 from which they are expelled in new combinations. 



" The parallel between a whirlpool in a stream and a 

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

 it is striking. The whirlpool is permanent, but the par- 

 ticles 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; as 

 they leave it on the other side, their places are made good 

 by new comers. 



" 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 



