130 C. M. JACKSON 



The brain weight has also apparently remained nearly constant 

 in the large group held at constant body-weight from three to 

 ten weeks of age. The average absolute weight is slightly less, 

 but almost in correspondence with the body-weight, so that the 

 average relative weight, 5.30 per cent, is nearly identical with 

 that of the controls at three weeks, the beginning of the experi- 

 ment. In terms of absolute weight, there is a very slight apparent 

 decrease from 1.274 grams (1.282 grams, less correction^ for 

 difference in body-weight, which averages 24.5 grams in the 

 three weeks controls and 24.0 grams at ten weeks) to 1.267 

 grams, a decrease of about 0.5 per cent in absolute weight. 



In the series held at constant body-weight from the age of 

 six to thirty-two weeks, there is an apparent slight decrease in 

 the brain from about 3.23 per cent to 3.14 per cent of the body, 

 and in the ten to thirty-five weeks series a slight increase (from 

 2.08 to 2.12 per cent) . Considering the small number of observa- 

 tions and the normal variation, however, these apparent differ- 

 ences do not appear to be significant. I would, therefore, con- 

 clude from the data above cited that there is probably no appreci- 

 able change in the weight of the brain in young albino rats held 

 at constant body-weight for considerable periods. 



Hatai ('04) experimented with a series of young rats with 

 initial body-weights corresponding roughly to those of mine at 

 the ages of six to ten wrecks. By giving an unfavorable diet 

 (starch and beef-fat) their body-weight was reduced on the 

 average about 30 per cent. The brain in these cases had appar- 

 ently lost in absolute weight, the average loss being about 5 per 

 cent. These results, however, are of course not directly com- 

 parable with those in which the body-weight has remained 

 constant. 



In a later experiment, Hatai ('08) by underfeeding with un- 

 favorable diet retarded the growth of a series of five rats, begin- 



3 It should be noted here as in other cases that the correction for organ-weight 

 is not in exact proportion to the difference in body-weight. Allowance must be 

 made for the change in the relative weight of the organ corresponding to the change 

 in body-weight. 



