SOME ANIMAL ARCHITECTS. 129 



But if the puzzle of life and of animal architecture is so 

 difficult of solution in these lower forms, it is found to present 

 no plainer aspects when offered for investigation in the per- 

 sonality and frame of even the highest being. Regarded 

 from an aspect similar to that in which the denizens of the 

 depths have just been studied, man's existence is seen to 

 comprehend phases of equally puzzling nature. No law of 

 life rests on a firmer basis than that which maintains that the 

 act of living and being is associated with constant change 

 and alteration, and that the wear and tear of life demand 

 proportional repair. Through each tissue of the body, 

 the life-renewing blood is therefore continually being dis- 

 tributed. The muscle, wearied in the actual work of the 

 body, recruits itself from the supply of nourishment thus 

 afforded it ; nerves renew their strength from the same 

 source ; and even thought itself thus becomes related in a 

 distinct manner to the material blood from which the think- 

 ing brain derives the wherewithal to carry on its work. Nor 

 is this all. It is not only the case that each tissue derives 

 from the blood the necessary matter to replace that which 

 has been lost and expended in the work of life. Each tissue, 

 it must be likewise noted, also takes from the common stream 

 of nourishment the materials necessary for the building up of 

 new substance. From the blood, bone selects the materials 

 necessary for the formation of new bone ; nerve from the 

 same source gathers matter for the production of new nerve- 

 tissue ; muscle therefrom elaborates new muscle ; cells of 

 wondrously diverse kind, like buyers of many nations in a 

 common market, select from the blood the special food or 

 pabulum suited to their wants, and therefrom manufacture 

 new cells : in short, the process of growth in man and in all 

 animals of higher grade, exemplifies the results of many varied 

 operations effected by the tissues and organs of the body 

 upon the common material offered to them, in the shape of 

 the nutrient blood. How this property of " selection " is 

 exercised, or what is its exact nature, science knows not as 

 yet. But the possession of this remarkable property of 



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