24 BULLETIN 106, U. S. DEPARTMENT OF AGRICULTURE. 
it is rarely delayed to a somewhat later period. After completion in 
its formation, that is, after its complete investment of the parts, it 
continues to grow in volume throughout pregnancy, the rounded 
projections at the internal os reaching in adult cows a diameter of 
2 inches. 
The uterine seal of the cow is a highly elaborate and interesting 
production apparently having as its office the simple function of a 
seal by which the uterine cavity with its contained young is hermeti- 
cally sealed and invasion from the vagina excluded. In the more 
than 1 ,700 pregnant cows and heifers examined on the killing floor 
the apparent efficiency of the uterine seal was well designed to excite 
admiration. The vagina might show marked evidences of long- 
standing infection, but the vaginal end of the uterine seal was firm, 
translucent, unstained, and to all appearances undisturbed by the 
infection. At its uterine end it was frequently stained by the hemor- 
rhages generally present at this point and at times its surface partly 
liquefied. When the exudate of abortion was present at the in- 
ternal os there was a more marked tendency to liquefaction of the 
uterine end of the seal, but in each case where the fetus was still intact 
and the membranes sound the body of the uterine seal revealed no 
changes whatever. It appeared as resistant to bacterial invasion as a 
living tissue; indeed it seemed more resistant than the neighboring 
mucosa. 
When the fetus was dead and decomposing the uterine seal was 
dissolved and had partially or wholly disappeared. 
The uterine seal is of especial significance in considering the avenue 
of infection and date of invasion in contagious abortion. 
During estrum the uterine cavity contains a considerable quantity 
of clear mucus. At or near the close of estrum, succeeding closely 
upon ovulation, in case impregnation fails to occur menstruation sets 
in. The mucosa then becomes injected, highly vascular, and swollen. 
The cotyledonal elevations of the mucosa enlarge, and from these a 
well-marked hemorrhage of bright-red blood occurs which later 
escapes per vulvam (menstruation). Should impregnation ensue, 
menstruation ordinarily fails, and the uterus continues large, soft, 
and smooth. The fertilized egg soon throws out its embryonic sac 
or afterbirth, so that when the embryo reaches the size of one-eighth 
of an inch the embryonic sac is already quite large, as thick and long 
as an ordinary lead pencil, almost colorless, very thin and delicate, 
lying wholly free within the uterine cavity without any visible trace 
of placental attachment. 
Later, when the embryo has reached a length of 2 to 3 inches, the 
placental attachments appear, at first very feeble, as faintly red 
patches on the chorion, gradually enlarging and thickening, the 
chorionic tufts becoming longer and more complex, while the coty- 
