WEIGHTS OF ORGANS IN UNDERFED YOUNG RATS 131 



ning at the age of 30 days, so that at 170 days their average weight 

 was only 91,5 grams, while full-fed controls averaged 146.5 

 grams. By comparison with 'second controls,' younger rats 

 of body-weight similar to the final weight of the stunted series, 

 he found that in the stunted rats the brain-weight was practi- 

 cally identical with that of normal rats of the same body-weight. 

 In other words, the growth in brain-weight had been retarded 

 in the same proportion as the body-weight. On this principle, 

 if the body-weight were retarded so as to permit no growth at 

 all, that is held at constant weight, we should expect practically 

 no increase in weight of the brain. This is in agreement with my 

 results, as above stated. 



More recently Donaldson ('11) has experimented with a larger 

 series (twenty-two litters) of rats held at nearly constant weight 

 (34 grams) from the age of thirty to the age of fifty-one days. In 

 the rats held at constant body-weight, the brain weight averaged 

 7.7 per cent less than in full-fed controls of the same litters. No 

 direct controls were taken at the beginning of the experiment, 

 but from the normal growth formula it is estimated that the 

 initial brain-weight was slightly less than that found in the 

 retarded rats at the end of the experiment. This would indicate 

 an increase of 3.6 per cent in the brain-weight, while the body- 

 weight was held constant. The large number of observations 

 lends weight to this conclusion, although it would be strength- 

 ened if direct controls were available at the beginning of the 

 experiment. 



It may be noted that if Donaldson's normal (Wistar reference 

 tables) rather than the direct controls be taken as the basis for 

 estimating the initial brain-weight in my three to ten weeks 

 series, the result would indicate a gain similar to that found 

 by Donaldson in his series. On the whole, therefore, we may 

 safely conclude that there is but very slight if any increase in the 

 brain-weight of young albino rats held at constant body-weight 

 for considerable periods of time. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 19, NO. 2 



