28 



S. HATAI 



ytill uourislicd nliuost entirely by mother's milk. According to 

 Donaldson ('0(3) the life span of the albino rat is about one- 

 thirtieth of that of man. Taking man's normal span as ninety 

 years and that of the rat as three years, we find that twenty- 

 one days of rat age corresponds nearly to the end of the second 

 year of childhood in man. Whether or not the dry substance 

 of the human body approaches 90 per cent of the maximum at 

 the end of the second year will be an interesting point to deter- 

 mine. Unfortunately this determination can not be made from 



Chart 1 Showing the growth of the dry substance of the albino rat during 

 its life span. 



the existing data. There are howe^'er in the literature data 

 on other mammals, and I have compiled the following table from 

 the data given by Aron ('15) to show the relative growth of 

 the dry substance in several other mammals contrasted with 

 such growth in the albino rat. 



On account of the lack of necessary data we are unable to 

 judge the growth rate of the dry substance in other mammals 

 during their suckling period. Nevertheless we note from table 

 5 that the rats are born in the most immature condition, so far 

 as the proportional weight of water and solids is concerned. 



