102 EFFECTS OF INANITION IN THE PREGNANT ALBINO RAT. 



By comparing the prenatal and newborn norms, it is found that the smaller 

 the fetus in utero, the smaller is the figure representing the body weight to body- 

 length ratio; in other words, the younger the fetus (from 2 to 4.1 grams), the less the 

 weight per millimeter of body length. The test rats follow this same law, the ratio 

 being very similar to that in the corresponding normal controls oi the same weight 

 or length. Therefore, it may be stated that the growth ratio, or the relation be- 

 tween fetal body-weight and body-length, is not disturbed by starving the mother 

 during pregnancy. 



Ratio of tail-length to body-length. -The ratio J^\^ ™ called the "toil 



ratio." In my normal newborns the tail ratio ( bod^ength, m"* mm. ) is °- 311 ( sexes 

 combined). Stewart (1918a), in litters from the same colony, found a tail ratio 

 of 0.318 (sexes combined). Jackson (1915a), using litters from both Minnesota 

 and Missouri, found a tail ratio of 0.36 in the newborn (sexes combined). The 

 tail ratio for the prenatal controls in Group I is 0.339 (all females) ; for the test 

 rats, 0.324; for the controls in Group II, 0.288, for the test rats, 0.310; for the con- 

 trols in Group III, 0.313, for the test rats 0.327; for the controls in Group IV, 0.300, 

 for the test rats, 0.326; for the controls in Group V, 0.296, and for the test rats, 0.323. 

 The tail ratio for the prenatal norm averaged for all five groups is 0.307; for the test 

 rats, 0.322, From these data it is apparent that the ratio of the tail-length to the 

 body-length during the later prenatal growth of the rat (from 2 to 4.1 grams) is 

 about the same as that found at birth; also that inanition in the mother during 

 pregnancy has very slight influence upon the tail ratio of the offspring. 



If the absolute data are directly compared, the tail-length in the test rats in all 

 the groups (table 5) is slightly above that of the prenatal norms of the same average 

 body-weight, being 2.8 per cent above in Group 1 and 13.1 per cent on Group V, 

 showing an average gam ol 6 per cent above the norm in all the groups combined. 

 This gain in tail-length, therefore, appears to be less marked in the smaller rats, 

 becoming greater as the size of the body approa ches that normal at birth. It agrees 

 with the observations of Jackson (1915a) and Stewart (1918), that postnatal star- 

 vation in growing rats tends to produce relatively long-tailed individuals. 



Head— Jackson and Lowrey (1912) give the weight of the head in the newborn 

 albino rat as 1.147 grams, or 21.65 per cent of the body-weight, 5.3 grams (sexes com- 

 bined) . In my normal newborn series the weight of the head is 1.041 grams, or 21.2 

 per cent of the body-weight, 4.92 grams. 



In my prenatal controls, the average weight of the head forms 24.2, 23.0, 22.7, 

 21.0, and 20.5 per cent of the body-weight in Groups I, II, III, IV, and V, respectively 

 (computed from table 5). Thus, in the prenatal controls, the head has a higher 

 relative weight in the smaller than in the larger rats, which fact agrees very well 

 with the law formulated by Jackson (1909) : "A relatively large embryonic head is 

 characteristic of vertebrates in general." The head in the smaller prenatal controls 

 also has a higher relative (percentage) weight than in the normal newborns, the 

 elifference decreasing with the increase in the weight of the prenatal controls. 



