24 S. HATAI 



were in good health. In all cases the contents of the entire 

 digestive tract were carefully removed before the body was 

 dried for further analysis. 



1. External bodily changes during the first six weeks of life of the 



albino rat 



A brief description of the external bodily changes during the 

 first six weeks of life may assist us to interpret some of the chemi- 

 cal changes which are in progress at this time. I shall there- 

 fore present a brief diary of this period. 



a. Rats are born naked. The eyes are closed. 



b. At the end of one week the skin shows a tinge of white 

 due to a growth of minute hairs. The eyes are still closed. The 

 body has more than doubled its initial weight. Milk is the ex- 

 clusive diet. 



c. At about fourteen or fifteen days of age the eyes open. 

 The body weight is more than three times that at birth. The 

 skin is covered with short hairs. Milk is still the exclusive diet. 



d. At twenty-one days after birth the rats are rinming about 

 the cage and occasionally eat bits of food present in the cage. 

 Thus the diet is mainly milk and in small part other food stuffs. 

 The hairs are long and the coat velvety. 



e. From this period on the rats grow without showing any 

 marked external alterations except the enormous growth of the 

 testicles in the males at the age of four to five months. 



We see from the foregoing that the greatest external changes 

 take place within the first three weeks, that is during the period 

 when the rats are feeding entirely on milk. It will be seen later 

 that the greatest changes in composition also take place within 

 this same brief period. 



2. Composition of the stomach contents 



As has been stated, milk is the exclusive diet of the rat for 

 the first three weeks of life, the period during which the most 

 important changes in the composition of the body take place. 

 It is highly desirable therefore to obtain data on the chemical 

 composition of the milk. Difficulty at once arises in obtaining 



