The Facts of Sex in Relation to Metabolism. 253 
plasm interferes with growth,” and half-humorously defines 
protoplasm as “the physical basis of advancing decrepitude”! 
We do not mean to wander from our subject to the extent 
of discussing this increased ratio of cytoplasm to nucleoplasm, 
nor the reason why growth should illustrate the law of 
diminishing return, but it will be useful to explain why we 
do not propose to accept Minot’s conclusion that from the 
period of birth there is “a steady loss of vitality.” 
Growth, as we understand it, means that anabolism is greater 
than katabolism. When growth is rapid the ratio = is a 
large one. As the animal grows older, it becomes more 
active, and it prepares for reproduction. It is evident that 
either by increase of katabolism, or by a transference of the 
results of anabolism from increase in bulk to other ends, e,g., 
reproductive, the rate of growth may diminish without there 
being any “loss of vitality.” And it is evident that a 
guinea-pig which has almost ceased to grow may have a 
more intense metabolism, more anabolism and more kata- 
bolism, in short greater vitality, than one which has lived 
only for a few days and is growing rapidly. In the former 
the ratio . will be less than the ratio = for the latter; 
but A will be greater than A’ and K greater than K’, and 
since vitality must be measured by the rate of the trans- 
formation of energy per unit mass, it is greater in the former 
than in the latter. 
But, furthermore, we are of opinion that Prof. Minot’s 
facts prove after all very little. For unless (1) the rate the 
taking in food (involving size of mouth, power of lowering 
air-pressure in lungs by diaphragm and ribs, etc.) and (2) the 
rate of assimilation (involving digestive, absorptive, and 
assimilative processes) were to increase at precisely the same 
rate as the weight of the young organism increases, it would 
be impossible for the rate of increase of weight to be constant, 
and since that rate of increase is destined to =0, the fact 
that the curve representing the rate of growth is a con- 
tinuously descending one is not in the least surprising. 
Surely, too, the conclusion that protoplasm interferes with 
VOL, XI. Ss 
