864 EXPERIMENT STATION RECORD. [Vol.35 



other investigators, this does not appear to be effective in the case of tlie 

 sulphur fraction of the molecule in the light of these experiments. " This con- 

 clusion is in accord with the present-day conception of the indispensability of 

 adequate amounts of preformed cystin in the diet, as recently exemplified by 

 the experiments of Osborne and Mendel on white rats." 



High nitrogen : sulphur ratios, with a retention of sulphur, were found during 

 the feeding periods following the fasting periods. When the feeding periods 

 extended over a number of days there occurred a gradual diminution of the 

 ratio to normal, but if the feeding period was followed by a fasting period the 

 ratios were lower than the normal or fasting ratios, indicating an excessive 

 elimination of sulphur as compared with nitrogen. On the basis of unpublished 

 experimental data, the author believes that this indicates a retention of sul- 

 phur to build up sulphur-rich tissues, as the result of a specific attempt of the 

 organism to restore material lost during the starvation period, rather than a 

 lag in the elimination of sulphur. 



ANIMAL PRODUCTION. 



Experimental studies on growth, II-VII, T. B. Robertson, L. A. Ray, and 



Ethel Cutler (Jour. Biol. Chem., 2// (1916), No. 3, pp. 363-Ji08. figs, l^; 25 

 (1916), No. 3, pp. 635-667, figs. 13). — In continuation of work already noted 

 (E. S. R., 35, p. 65), six papers are here presented on the influence of protein 

 dietary factors upon the process of growth and phenomena incident thereto in 

 white mice. 



II. The normal growth of the ivhite mouse (pp. 363-383). — In these studies 

 it was found that " in each sex there are three separate extra-uterine growth 

 cycles. The first cycle attains its maximum velocity at some time shortly 

 prior to 7 days after birth and culminates at 14 days. The second cycle attains 

 its maximum velocity at from 21 to 23 days and culminates soon after the 

 twenty-eighth day. The third cycle attains its maximum velocity at about 6 

 weeks and thereafter decreases in velocity continuously but very slowly, so that 

 growth of the animals still occurs between the fiftieth and sixtieth weeks suc- 

 ceeding birth. 



"All the cycles are less extensive in the female than in the male. 



" The variability in weight of the animals shows a decided tendency to in- 

 crease with increasing velocity of growth and to decrease with decreasing 

 velocity of growth. After the fortieth week, however, especially in the females, 

 there is a tendency of the variability to increase progressively without any cor- 

 responding increase in the rate of growth. 



" Weaning of the animals on the twenty-first day after birth produces no 

 physiological disturbance whatever in the young. 



" It is shown from the variability of the weight that considerable numbers 

 of animals must be employed to obtain reliable data in experiments upon 

 growth. The weight data reported in this and succeeding articles are probably 

 within 1 or 2 per cent of the true values. 



" Birth in mice occurs during the first half of the first growth cycle. The 

 eyes open coincidently with the culmination of the first growth cycle, a com- 

 plete coat of fur being acquired at the same time. Puberty coincides with the 

 period of maximum velocity of growth due to the third growth cycle. 



"The development of the thyroid and of the thymus in mice presents well- 

 marked stages which coincide closely with the cycles displayed in the growth 

 curve of these animals. Subsequent to the culmination of the first-gi-owth cycle 

 the thyroid is heavier in the male than in the female, while the thymus is 

 heavier in the female than in the male. 



