36 CHESTER A. STEWART. 



9. Brain (Table V.}. 



The brain shows but little deviation from Donaldson's ('15) 

 Wistar norm for rats of same body length in either the rats 

 killed at the end of maintenance or in those refed for various 

 periods. Such slight fluctuations from the norm as are shown in 

 the table are probably within the range of normal variation. 

 Jackson ('15) noted that there was practically no change in the 

 brain weight of young albino rats held at constant body weight 

 for considerable periods. 



It may therefore be concluded that the brain weight is normal 

 in the young rats at the end of the maintenance period, and 

 remains normal throughout the period of refeeding. 



10. Spinal Cord (Table F.). 



The weight of the spinal cord in the two rats killed at the end 

 of the maintenance period exceeded Donaldson's norm, 34.3 and 

 19.9 per cent. This confirms Jackson's ('15) observation that 

 the spinal cord shows a marked growth in young rats held at 

 constant body weight. 



On refeeding, this excess weight (as compared with normal for 

 corresponding body length) rapidly disappeared, so that by the 

 end of the first week the weight of the spinal cord exceeds 

 Donaldson's norm only 7.3 and 3.2 per cent, in the I male and 4 

 females respectively. Thus the spinal cord had nearly regained 

 the normal proportion. 



At the end of two and four weeks of refeeding the weight of 

 the spinal cord was slightly below the Wistar norm, as was also 

 true of the controls at sixteen weeks of age. This condition 

 therefore appears to be normal for my series of rats and not an 

 experimental modification. 



In the test rats (refed after maintenance for various periods) 

 killed at the age of one year the weight of the spinal cord was 

 normal as compared with the controls, although in each case the 

 average weight was 8 to 10 per cent, heavier than Donaldson's 

 norm. 



In general therefore the results indicate that the spinal cord, 

 which was relatively heavy at the end of the maintenance period, 

 returned to the normal proportion during the first two weeks of 

 refeeding, and remained normal after that time. 



