A STUDY ON THE RELATIVE GROWTH IN THE BODY OF ALBINO RATS

Abstract

It would be evident from the preceding data that the rates of growth are not uniform with every part and organ of the animal's body. To summarize the whole data, however, it would be concluded that the rate of growth in the body weight during the fetal period and directly after birth is especially pronounced and that the increases in the weights of every internal organ was larger than those in the other parts of the body. As shown in Table 26, the relative growth rates also differ between each part and organ of the body. The largest α value obtaind is 5.02 in the body weight in animal's fetal period, followed by 2.42 in the body weight after birth of the animals. (Fig. 26) As for the growth rates of bones, the value α of the lower extremities is comparatively large showing the values 1.41 to 1.58, while that of the upper extremities slightly falls behind with the values 1.21 to 1.28. (Fig. 41) The bones in the head and face are poor in the growth rate in comparison to the growth rate of body length showing 0.52 to 0.89, values smaller than 1.0. Of the relative growth rates of the internal organs, the smallest is the value 0.58 for the lung, followed by 0.99 for the heart, both showing growth lesser than that of the body weight. On the contrary, the values 1.06 for the spleen, 1.12 for the stomach and the liver, 1.15 for the kidneys, 1.24 for the thymus, these values show that all these organs slightly exceed the body weight in the growth rates. It has been known from reviewing the works of previous investigators that Shimizu had also studied the coefficients of relative growth in albino rats utilizing the combined data accumulated by Negishi and Watanabe concerning the tail, by Tappe concerning the body weight and by Donaldson concerning the various organs. The α values 2.28 to 2.29 which Shimizu has given as the relative growth coefficient of the body weight against the head to tail-root length is fairly comparable with the author's value 2.42. Unfortunately no report being available as to relative growth of any part or organ of the rat embryo, the present author's value 5.02 was here given which showed a vigorous growth rate occurring in the fetal life of the animal. Of the relative growth rates of various internal organs against the body weight, Shimizu, concerning the heart, has given the values from 0.77 to 1.03 regardless of sex difference of the animal, and Clark has given the value approximately of 0.8 in the mice, rabbits and dogs. These are closely comparable with the author's value 0.99. Of the lung Shimizu, in the albino rats, gave the values from 0.70 to 0.84, Brody, in the dog, 0.85 and the present author 0.58. Of the stomach Shimizu gave values from 0.63 to 1.34 in the albino rats, Brody 0.72 of the stomach and the intestine in the dogs and the present author 1.12 in the albino rats showing a slight difference present between these data. Of the liver Shimizu gave values from 0.75 to 1.81, Brody 0.7 in the dogs and the present author 1.12, an intermediate value of Shimizu's data. Of kidneys Shimizu gave values from 0.81 to 1.75, while the present author gave 1.15. Of spleen Shimizu's value were 0.93 to 1.56 and the present author's 1.06. As shown above, the comparison of the author's data on the relative growth rates of internal organs against the body weight with those of the previous authors proves that there is general agreement between these except minor differences observed between two or three different organs. According to Shimizu's opinion the α value of the internal organs did not change appreciably after the animal's body weight reached approximate value of 35g, and Donaldson added further that 35g of body weight was gained at the 34th to 35th day after birth of the animal and that this corresponded also to the 3rd molar eruption. The present author also confirmed that the animals weighed about