THE WHIRLPOOL OF LIFE. 85 



Those who have seen the wonderful whirlpool, three 

 miles helow 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 

 contour of its crest, this wave has been visible, approxi- 

 mately in the same place, and with the same general 

 form, for centuries past. Seen from a mile off, it would 

 appear to be a stationary hillock of water. Viewed closely, 

 it is a typical expression of the conflicting impulses 

 generated by a swift rush of material particles. 



Now, with all our appliances, we cannot get within 

 a good many miles, so to speak, of the crayfish. If we 

 could, we should see that it was nothing but the constant 

 form of a similar turmoil of material molecules which 

 are constantly flowing into the animal on the one side, 

 and streaming out on the other. 



The chemical changes which take place in the body of 

 the crayfish, are doubtless, like other chemical changes, 

 accompanied by the evolution of heat. But the amount 

 of heat thus generated is so small and, in consequence 

 of the conditions under which the crayfish lives, it is so 

 easily carried away, that it is practically insensible. The 

 crayfish has approximately the temperature of the sur- 

 rounding medium, and it is, therefore, reckoned among 

 the cold-blooded animals. 



If our investigation of the results of the process of 



