POSTNATAL GROWTH IN THE ALBINO RAT 



27 



6. Heart 



According to the curve of relative (percentage) weight (fig. 1 a) 

 constructed from Hatai's formula, the heart increases from 0.64 

 per cent of the body weight at 5 grams to a maximum of 0.70 

 per cent at 10 grams. Thereafter it gradually decreases to 0.67 

 per cent at 20 grams, 0.56 per cent at 50 grams, 0.45 per cent at 

 120 grams, 0.42 per cent at 170 grams, and 0.40 per cent at 200 

 grams, 0.37 per cent at 300 grams and 0.35 per cent at 400 grams. 



When grouped according to age periods, my own data (table 7, 

 fig. 1 a) show an increase from an average in the male of 0.65 per 

 cent at birth to 0.68 per cent at seven days and to a maximum 

 of nearly 0.73 per cent at twenty days; thereafter it decreases 

 to about 0.45 per cent at one year. In the female the relations 

 are similar, although the average relative weight is greater at 

 every age (except twenty days). This apparently greater rela- 

 tive weight of the heart in the female, however, is probably with- 

 out significance. In the first place, the relative weight of the 

 heart in the female at any given age beyond six weeks should 

 be slightly greater on account of the smaller body weight. More- 



5 10 20 



150 

 Body weight m grams 



