6 



BULLKTIX 1121, U. 



DEPAETxMENT OF AGRICULTURE. 



A? f^ 7- 9 /0-/2,J-3 f-6 7^3 /(HZ, ,h3 f-e 7-9 /t^/^ ,A? 4-6 7-9 X)-/Z, 

 ~7S?^ /9/7 /9/3 /3/9 



Fig. 1.— The percentages horn alive, raised of those born aJive, and 

 raised of all young, in the inbred stock during successive 3-month 

 periods, 1916-1919. 



averages is given in Table 27. The results are presented graphically 

 in Figures 1 to 7. The periods of depression and of good condition 



are clearly brought 

 out . In a general way 

 there is agreement be- 

 tween the fluctuation 

 of the percentage born 

 alive, the percentage 

 raised of those born 

 alive, birth weight, 

 rate of gain, and size 

 and frequency of lit- 

 ters. Figure 6, which 

 shows the number of 

 young raised per year 

 by the average mating 

 in each period, per- 

 haps reveals best the 

 changes in environ- 

 mental conditions. 

 The probable absence 

 of relation between sex ratio and season may be seen by comparing 

 Figure 7 with Figure 6. 



There are various ways in which allowance could be made for these 

 fluctuations. The method which has been adopted is to compare 

 the actual average or 

 index for each experi- 

 ment for the entire 

 period in which it 

 was maintained with 

 the estimated record 

 of the total inbred 

 stock produced simul- 

 taneously. As an ex- 

 ample, we see in Table 

 22 that there were 0.3 

 mature matings in Ex- 

 periment Cl in the pe- 

 riod July-September, 

 1916. The record of 

 the inbreds as regards 

 frequency of litter dur- 

 ing this period is given in Table 2V as 3.35. Multiply these together 

 and add the similar products for subsequent periods in the history 

 of Cl . On dividing by the total number of mature matings (3 months' 



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,AJ 4-S 7-9 /(HZ, , h3 4-ff 7-9 /0-/2„/-J -^^ 7-9 /0S,/y3 4^ 7^9 , 



TSTe 7¥?7 /&/a T^TW 



Fig. 2. — The average birth weight of young raised to weaning (33 days) 

 and of all young born in the inbred stock during successive 3-month 

 periods, 1916-1919. 



