34 . S. HATAI 



same as that given by the albino rat at birth are contrasted 

 with one another without regard to either calendar age or body 

 weight. Similarly in the four remaining groups the animals 

 whose bodies gi\''e an amount of water nearly the same as that 

 of the rat at 7, 15, 32 and 294 days respectively are also compared. 

 The table may be analysed from various standpoints. 



1. Age and body iveight. Despite the fact that the percentage 

 of water in the body is practically the same in the several entries 

 composing a group, the corresponding ages or body weights vary 

 widely in the different species. 



This fact may be taken to mean that the different species 

 have a dissimilar rate of growth in body weight and require 

 different intervals of time in order to pass through the several 

 values for the percentage of water which lie between the two 

 limiting values of 88 per cent and 65 per cent found in all mam- 

 mals so far examined. Thus the percentage of water on the 

 one hand and body weight or age on the other are not similarly 

 related in the mammalian series. 



2. Percentage composition of solids. On the other hand if 

 we compare the percentage composition of the solids (protein, 

 fat and ash) given by the various mammals, when they possess 

 a like percentage of water, a surprising uniformity is shown. 

 In general, similarity in the percentage of water gives similarity 

 in all the other main chemical components. A slight tendency 

 to an increased variability -as shown by the older animals seems 

 due to several analytical difficulties — represented by complete 

 drying and the extraction of fat. Thus it appears probable 

 that a uniform technique and also a vigorous selection of healthy 

 individuals would tend to smooth out the irregularities now 

 shown in this table. 



Despite the presence of some irregularities, we see plainly 

 that following the progressive diminution of the percentage of 

 water, the percentage values of protein, fat and ash increase 

 regularly. Furthermore, this reciprocal relation of water and 

 other chemical groups is so harmonious that we are strongly 

 tempted to conclude that there is a definite quantitative rela- 

 tion similar in all mammals in their chemical make up at equiva- 

 lent ages. 



