POSTNATAL GROWTH IN THE ALBINO RAT 31 



* 8. Liver 



The curve representing the relative (percentage) weight of the 

 liver, according to calculations from Hatai's formula, is shown 

 in figure 6 a. It is seen that the relative weight of the liver 

 increases from 4.87 per cent of the body weight at 10 grams to 

 a maximum of 7.80 per cent at 25 grams, after which it gradually 

 decreases to 7.17 per cent at 50 grams, 5.75 per cent at 120 

 grams, 5.02 per cent at 200 grams, 4.55 per cent at 300 grams, 

 and 4.27 per cent at 400 grams. 



When grouped according to age periods, my own data (table 

 9, fig. 6 a) show that in the male the relative weight of the liver 

 forms an average of 4.74 per cent of the body weight at birth. 

 Unlike the organs previously considered, it apparently decreases 

 at seven days, to 3.39 per cent, increasing to 4.64 per cent at 

 twenty days and reaching a maximum of 6.78 per cent at six 

 weeks. Thereafter it decreases to an average of 4.42 per cent at 

 one year. The female exhibits a similar course of growth; but is 

 slightly larger relatively than the male at birth and seven days, 

 and smaller at all later periods.* My data therefore indicate a 

 sexual difference, although none was found by Dr. Hatai in his 

 data. 



It will also be noted that the liver in my data is at all periods 

 relatively small, when compared with the formula derived from 

 Hatai's data. It is possible that the discrepancy may be due to 

 a slight difference in the diet. Chalmers Watson ('10) finds a 

 marked decrease in the relative size of the liver in captured wild 

 rats, and ascribes the decrease to a diminution in the protein of 

 the bread and milk diet during captivity. If the lower figures 

 in my data were due to this cause, however, we should expect to 

 find a similar condition in the kidneys, which Watson finds also 

 to be larger with rich protein diet. As will be seen later, how- 

 ever, my data usually show for the kidneys a higher relative 

 weight than that according to the formula calculated from Hatai's 

 data. The difference, therefore, can hardly be explained on this 

 basis. 



