Rohan)" e civaree | | 
6 BULLETIN 1121, U. S. DEPARTMENT OF AGRICULTURE. | 
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. Inageneralway | 
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 
Fie. 1.—The percentages born alive, raised of those born alive, and chang es in environ- 
raised of all young, in the inbred stock during successive 3-month mental conditions 
periods, 1916-1919. ; 
AGAE #3 3 102 I “ res MG1e, fF? <i oe Mele f3 #6 PI 12 
79/9 
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 seein Table 
22 that there were 0.3 
NSE 
FMT 
mature matings in Ex- ue » 
periment C1 in the pe- REGUABEREDe 
riod J uly—September, O° $5 79 Wie IF 46 79 Whe ee a = lle £3 FE6_79 M-Ls 
Tats (EE ate 
7S/7 1919 
1916. The recor d of Fic. 2.—The average birth weight of young Riere to weaning (33 days) 
the inbreds as regards and of all young born in the inbred stock during successive 3-month 
frequency oflitterdur- P70 181° 
ing this period is given in Table 27 as 3.35. Multiply these together 
and add the similar products for subsequent periods in the history 
of C1. On dividing by the total number of mature matings (3 months’ 
