10 BULLETIN 1121, U. S. DEPARTMENT OF AGRICULTURE. 
nate represents the percentage of deaths, to the other side, survivals. 
The change in the percentage of deaths due to a given shift in the 
conditions is equal to the area between two ordinates at a given dis- 
tance apart. This area is of course greater at the middle of the 
curve (50 per cent deaths) than toward either limit. On this hypoth- 
esis a table of probability integrals can be used for comparing per- 
centage differences at different points of the range between 0 per cent 
and 100 per cent. 
The numbers in Table 2 give the departure of each experiment 
from the total inbred stock, adjusted on the above basis to the record 
of the latter for the whole four years 1916-1919, 1. e., 77.7 per cent 
born alive, 72.1 per cent raised of those born alive, and 56.3 per cent 
raised. This correction, it will be noticed, makes the records of AC 
and CC, with which this discussion started, approximately equal. 
So far as most of the conclusions are concerned, it makes little differ- 
ence whether the correction is made or not. It seems important, 
however, to show the order of effect. 
ALLOWANCE FOR HEREDITY. 
Another consideration, which has doubtless occurred to the reader 
m comparing the records of the inbreds and crossbreds, is the exact 
heredity of the latter. There are fairly large differences among the 
inbred families themselves. If only animals from the better families 
were used in making crosses, the latter would naturally be superior, 
apart from the effect of the system of mating. 
TaBLE 3.—The inbred ancestry of the males and females used in the various crossbreeding 
experiments, in percentages. 
[Each mating weighted by the number of litters produced through 1919.] 
CO. | CC. CA. AC. 
inbred tamily.e) | | len an@2: 
Sire. | Dam. | Sire. | Dam. | Sire. | Dam. Sire. | Dam. 
DE oki wre eae Ras A 16.1 19.3 9.7 8.0 5.4 5.8 20.9 18. 4 16.9 27.0 
ee eae yee Tee 7.7 23.6 16.1 8.0 16.3 PAST 21.8 42.4 18.0 15. 2 
Yah Sate te ia Baie See FF iy) ta2 4.2 5.3 5.6 2.9 8.5 26. 6 IES 7; 7.0 
SOREN ECEE Pa hee infil eal 6.5 0 We 4.2 9.8 12.0 Dine 7.0 
OE eee eee te tee 16.6 7.9 18.3 18. 7 21.0 W757 IW Ad/ 0.6 17.4 17.3 
CRS Ben hl en One 4.8 PU 0.6 0 1.0 a 0 0 0 gue 
Qi Say a weees, eee late ey 3.1 3.8 4,7 3) 0 1.0 0.9 0 0 2.0 
dW fest jeune tae adh Ot — 3.8 6.8 8.7 12.0 6.5 1.0 i168} 0 3) 0.6 
PS MIPS £8 AIOE S 4.1 qi 3.0 0 0.6 45) UPR: 0 0 2.9 
7 ee 9 OTN ee a 4:1 6.5 3.6 8.0 35) 5. 8 Day 0 0 5.3 
Pee te eee 7.0 2.1 2.4 0 7.9 4.2 20 0 0 Piz 
CET pte Se rote 0 0.9 0 0 0 0 1.3 0 0 0 
SETURL Ty PEGE 4.6 Qe. 4.4 10.7 4.0 5.0 1.6 0 0 aa 
BS be dee ae Ean 3.8 IS 76 2.8 0.7 10.5 7.9 9.5 0 0 re 
SOR Res ee EE Ee Th) 4.1 6.7 8.0 5.4 4.0 0 0 0 4.7 
Yoana sp iey S ee Se ae Re ayers 2.4 4,4 8.3 15.3 4.8 11.8 0.3 0 2 ane 
(Of Gage eit alee teria 43.2 36.9 45.2 60. 0 44,2 45.7 21.3 0 4.7 26.5 
As it was, however, an effort was made to use all of the families, 
So far as any preference was given it was to the weaker ones. The 
inbred ancestry of the sires and dams of the litters produced in each 
