THE WHIRLPOOL OF LIFE. 85 
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 
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 astationary 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 
