110 C. M. JACKSON AND C. A. STEWART 



only 59 grams at 513 days. Rapid growth ensued upon full 

 refeeding, the body weight reaching 220 grams, which is above 

 the normal maximum, in about 130 days. Unfortunately, no 

 direct controls from the same litters were kept in the experiments 

 of Osborne and Mendel. They admit that ''resumption of 

 growth has not been as perfect in every case as in the typical 

 records here presented," but the positive results are considered 

 more valuable, since failure may be due to various causes. 

 Their results will be referred to again later. 



As to the variation in the effect of inanition according to the 

 age of the animal, it is evident from charts 1 and 2 that under- 

 feeding beginning at birth produces permanent stunting, whereas 

 Stewart ('16) found that an equal (or greater) degree of under- 

 feeding for similar periods beginning at three weeks of age is 

 followed by complete recovery of body weight upon later full 

 refeeding. As previously mentioned, Briining likewise appar- 

 ently obtained a permanent retardation of growth of nursing 

 rats. It is not strange to find that a permanent stunting is 

 more readily obtained in younger animals (probably likewise 

 in the human species), when the normal growth process is most 

 active and the organism in general is less resistant to starva- 

 tion. The greater power of recuperation found by Osborne and 

 Mendel is probably due in part to the fact that their rats were 

 underfed beginning usually at five weeks or more of age, at 

 which time their resistance to inanition is greater. 



In this connection it is of interest to note that both Dunn 

 ('08) and King ('16) found that rats greatly undersized at birth, 

 although they may grow vigorously for a time, usually fail to 

 reach the normal adult size. In these cases, King assumes 

 that "The normal action of growth factors is inhibited from the 

 very beginning of postnatal life by unknown constitutional 

 causes, not by environmental conditions." It seems to be quite 

 possible that in such cases the small size at birth may be due 

 to prenatal malnutrition, which might be expected to exert a 

 more detrimental effect during the earlier stages of the 

 organism. 



