30 



S. HATAI 



The composition of the dry substance 



l)(>tiniti()iis of the terms used for the fractions of the dry sub- 

 stance recorded in table 6 are given in the following paragraphs. 



TABLE 6 

 Showing the percentage composition of the solids of the albino rat during the life 

 span, as represented by the residue, fats, organic extractives, soluble salts and 

 fixed salts 



Residue 



Percentage of moist weight 



Fat 



Percentage of moist weight. 



Organic extractives . . . 

 Percentage of moist weight 



Soluble salts 



Percentage of moist weight 



Fixed salts 



Percentage of moist weight 



294 



44.5 

 15.5 



16.5 

 5.7 



28.2 

 9.8 



2.5 

 0.8 



8.3 

 2.9 



1. Residue. The residue is represented by the solids from 

 which all substances soluble in boiling alcohol and in water, as 

 well as the salts, have been removed. Thus the residue as here 

 defined represents practically all the protein substances. As 

 will be seen from the table, the residue expressed as a percentage 

 of the moist ( = total) weight increases steadily from birth on- 

 wards. However the residue considered as a fraction of the 

 dry solids is highest at birth and diminishes gradually until the 

 end of the lactation period, after which it rises again. This 

 change in the relative residue content is probably caused by 

 the variations in the proportion of fat. 



2. Fat. Fat is represented by the substances, soluble in boil- 

 ing alcohol, from which the water soluble organic extractives 

 and salts have been removed. From the table we find that the 

 rat at birth has a verv small amount of fat. The fat however 



