Effects of Rate of Growth on Post-natal Development of the White

Abstract

In order to investigate the reactions of the various organs of the body to a radical acceleration in growth rate, over 200 male albino rats of a homogeneous pedigreed strain were fed in such a way that one-half of them grew approximately twice as fast as the other half. This increase in rate of growth was effected by adding greater amounts of yeast and lettuce to an already adequate diet, hence the “slow ”growth (animals were not stunted but themselves grew somewhat faster than the standard given by Donaldson. At body weights of 60, 90, 120, 150, 180, 240, 300, 360, 420 and 480 gm., 10 rapid and 10 slow growth rats were killed and studied.

A comparison of the 2 groups of rats gives the following results: (1) The ratio between body length and body weight is the same at any given length or weight for both the rapid and slow growth rats and also for Donaldson's animals. (2) The size (measured in terms of wet weight) of 3 different muscles, of the kidney, spleen, thyroid and pituitary depends upon the size of the rat and not upon its age. The same is true, in the main, of the heart and liver, but there is a definite tendency for the rapidly grown rats to have larger livers and hearts than the slowly grown ones of the same body weight. (3) The size of the eyeballs is a function of age rather than body size, furthermore the growth of the eyes in both rapid and slow growth rats is “heterogonic ”and differently so in each case. Rats grown rapidly up to adult size and then maintained at that point until as old as slow growth rats that have just reached full stature have eyes as large as those of the slow growth animals.