404 THE WONDER OF LIFE 



income, but a periodic controlled increase, differing in its 

 rate in different species and at different times, and proceeding 

 in such a way that what we call proportion is secured. 

 Professor Kelhcott, in an important contribution to the 

 theory of growth, has emphasized the same idea by calling 

 attention to the diversity in the rate of growth of different 

 parts of the body. 



In the smooth dogfish (Mustelus canis) the various organs, 

 or perhaps tissues, seem to grow characteristically, each 

 having an individual form of growth curve. The rates 

 of growth of the brain, the heart., the pancreas, the spleen, 

 and so on, are different from the rate of increase in total 

 weight. Indeed, it seems to Professor KeUicott that in 

 fishes, which are organisms of indeterminate growth, the 

 brain, heart, digestive glands, and fins do not always keep 

 pace with general increase of trunk musculature and connec- 

 tive tissue, and a loss of functional equilibrium results. The 

 fish may grow too large for its heart or for its brain. It 

 cannot be doubted that the determinate growth of birds 

 and mammals is an improvement on the more primitive 

 unhmited growth of fishes, which is less perfectly regulated. 



When we consider growth in its entirety as a regulated 

 seK-increase of the whole organism and of its parts, we 

 see how far it hes beyond the present limits of physico- 

 chemical interpretation. The analogous phenomena of 

 chemical polymerization and of the increase of crystals 

 in a solution are certainly interesting, but they do not 

 seem to have brought us more than a httle way nearer 

 understanding organic growth. That an organism should 

 keep its own diary, entering therein its tradings with 

 time, is just a particular case of what is either a wonder or a 

 commonplace, that a hving creature is characterized by this 



