8 BULLETIN 1121, U. S. DEPARTMENT OF AGRICULTURE. 
ing. The records in four previous years, 1911-1915, as well as in > 
| 
these years show that the total inbred stock rose and fell in 
| close parallelism with | 
2.60 
2/0 
4 
13 FC 79 1012 63 #E 7-2 1012 
9/6 19/7 
Fic. 5.—The average size of litters produced by the inbred stock in 
successive 3-month periods, 1916-1919, 
had been available. 
As it was, 
43 #6 7-9 101EI3 FEC 79 1072 
er ea ee es 
the control stock. 
The rising records for | 
the years 1916-1919 | 
certainly give no evi- | 
dence of continued | 
genetic decline. It 
would have been de- 
sirable to have used — 
only one family as a 
criterion of the rise 
and fall in environ-— 
mental conditions if | 
sufficient numbers — 
it seemed best to use the total | 
inbred stock. This stock was largely composed of five families - 
which were kept up to about the same proportional represen- 
tation during this 
period. The com- 
bined averages for 
the other families, 
moreover, were close 
in most respects to 
the average of these 
five important fami- 
lies. 
A comparison of 
the entries in Table 
28 with the corre- 
sponding onesin Table 
29 brings out, it is be- 
lieved, the superiority 
or inferiority of each 
experiment to the 
total inbred stock, 
free from the influ- 
ence of seasonal fluctuations and of size of litter on the other char- 
acters. 
Ord FE 7-9 10-1 
HO 
RRREGES 
IAT 
CALTON ATE 
PAP ARR AUT 
AALWEE LT 
LPT 
SERRA RR RRRRREEDE 
C9 FC 72 DIE GF. FO TI WI 
4H/. Teer 
FO PI SVE SLI FE FI Gc cl cle I 
ee mEyoc. 
Fic. 6.—The average number of young raised per year, by mature mat- 
ings, inbred stock, during successive 3-month periods, 1916-1919. 
