20 BULLETIN 106, U. S. DEPAKTMENT OF AGRICULTURE. 
Table 3. — Average periods of incubation of abortion. 
Species, source of data, etc. 
Number of 
animals. 
Average 
period of 
pregnancy 
when inocu- 
lated. 
Average 
time of 
termination 
of pregnancy. 
Average in- 
terval be- 
tween inocu- 
lation and 
termination 
of pregnancy. 
Cows. 
British Royal Commission: 
Complete abortions 
1 
3 
Days. 
71 
103 
37 
61 
Days. 
189 
254 
Days. 
118 
151 
135 
Premature births 
Killed when abortion was apparently threat- 
ened 
Average for 3 classes 
11 
5 
1 
4 
1 
65 
69 
141 
1 
45 
113 
101 
190 
174 
199 
199 
128 
167 
107 
126 
106 
58 
199 
83 
Killed without symptoms of abortion 
New York State Veterinary College: 
Complete abortion 
Prof. B. Bang citing Poulsen: 
Cows infected by bull 
Ewes. 
British Royal Commission: 
Complete abortion 
Lambing (3) or dying at full term from torsion of 
uterus ( 1 ) and showing abortion bacilli 
54 
Killed without aborting before full term and 
showing abortion bacilli 
6 
Guinea pigs. 
British Royal Commission: 
Aborted and abortion bacilli recovered 
Aborted, but abortion bacilli not recovered... 
1 
4 
Undet. 
Undet. 
Undet. 
Undet. 
19 
10 
5 
2 
Undet. 
34 
Undet. 
53 
12 
Bitches. 
British Royal Commission: 
Aborting, but no abortion bacilli recovered. . . 
20 
3. The data upon the duration of incubation in the cow vary in 
such a manner as to invite grave doubts as to the reasonableness of 
the conclusion that the artificially introduced abortion bacillus caused 
the abortion. Referring again to Table 3, we find that the constancy 
of the average date of pregnancy at which the cows of various experi- 
menters aborted is remarkable — 5 by Dr. Moore at the New York 
State Veterinary College, averaging the one hundred and ninety-ninth 
day; 11 by the British Royal Commission, averaging the one hundred 
and ninetieth day; 7 by Poulsen, cited by Bang, the one hundred and 
ninety-ninth day; and 3 by Bang the two hundred and fourth day. 
In the column recording the period of incubation the same lots 
show 126, 58, 199, and 114 days, respectively, which gives a very 
wide and inexplicable variation until a comparative study is made of 
the date of inoculation. It then appears that the period of pregnancy 
at which abortion occurred suggests that the duration of incubation 
is dependent upon the date of inoculation. In other words, inoculate 
pregnant cows at any date one likes, the average date of pregnancy 
at which abortion occurs remains the same. We might say that, 
according to recorded data, the inoculation at any time of a pregnant 
