EFFECTS OF INANITION IN THE PREGNANT ALBINO RAT. 107 



the skeleton (with musculature) is but 6 per cent (Stewart, 1918a). This seems to 

 show that the growth tendency in the skeleton is relatively weak at birth, which 

 may explain its apparent loss of weight in my test rats. 



In my normal newborn series the weight of the dried skeleton is 0.089 gram or 

 1.8 per cent of the body-weight, 4.92 grams. Conrow (1915) found the dried 

 skeleton to be 1.9 per cent of the body-weight in the normal newborn rat (body- 

 weight, 4.2 grams; calculated weight of dried skeleton, 0.081 gram). 



In my prenatal controls the weight of the dried skeleton forms 1.4, 1.5, 1.5, 1.7, 

 and 1.6 per cent of the body-weight in Groups I to V, respectively (computed from 

 table 5). Thus the dried skeleton in the prenatal control has a relative weight 

 slightly below that of the normal newborn rat. 



In my test rats the weight of the dried skeleton forms 1.5, 1.8, 1.7, 1.8, and 1.7 

 per cent of the body-weight in Groups I to V, respectively (computed from table 5) . 

 Thus the relative weight of the dried skeleton in the test rats is slightly higher than 

 in the prenatal controls. 



Concerning the absolute weight of the dried skeleton, however (see table 5), 

 the results obtained are different from those in the case of the moist skeleton. 

 Although in Groups I, II, and III (see table 5) the absolute weights of the moist 

 skeletons in the test rats were 27, 1.8, and 5.0 per cent below the prenatal controls 

 of the respective groups, and 0.4 and 0.01 per cent above in groups IV and V, re- 

 spectively, the absolute weight for the dried skeleton of the test rats exceeds that of 

 the prenatal controls in all five groups, the excess being 7, 20, 14, 9, and 9 per cent, 

 respectively, from Group I to V (see table 5), averaging 12 per cent above for all 



groups. 



This increase in the weight of the dried skeleton in the test rats is evidently due 

 to an increase of dry substance in the bones, cartilages, and ligaments. Therefore, 

 since the dry skeleton shows a relatively greater increase in the test rats as compared 

 with the prenatal controls of the same body-weight, it is apparent that, although the 

 body-weight is retarded, the relative percentages of solid substance and water in the 

 test rats tend to approach that found in the normal newborn rat. The tendency 

 of the skeleton to grow in mass (although at a retarded rate) in cases of underfeeding 

 in rats was observed by Jackson (1915a) and by Stewart (1918). Lowrey (1913) 

 found that in the postnatal growth of the rat the amount of dry substance in the 

 ligamentous skeleton increases with age, being 18.1 per cent at birth, 33.3 per cent 

 at 20 days, 39.2 per cent at 6 weeks, 45.9 per cent at 10 weeks, 50.4 per cent at 5 

 months, and 52.6 per cent at 1 year. 



No observations were made on any of the skeletons to determine whether there 

 was any variation in the normal process of differentiation (developmental changes) 

 between tha test rats and prenatal controls. Jackson (1915a) and Stewart (1918), 

 however, found that during maintenance of body-weight by underfeeding in young- 

 rats, skeletal growth and differentiation occurred apparently in a normal manner, 

 although at a retarded rate. 



