26 BULLETIN 106, TJ. S. DEPARTMENT OF AGRICULTURE. 
there appears at the periphery of many placentae a pale yellowish- 
gray zone, very narrow, but showing a marked variation in color 
from the other parts. The pale zone upon examination consists of 
chorionic tufts which have been withdrawn from the cotyledonal 
crypts, and the tufts, losing their placental contact and function, 
become nonvascular and present a necrotic appearance. Their 
appearance suggests mechanical separation during the to-and-fro 
movements of the fetal sac within the uterine cavity. 
THE NECROTIC TTPS OF THE FETAL SAC. 
The cornual prolongations of the fetal sac grow out very quickly 
against the apices of the cornua and are longer than the cavities they 
occupy, so that they become crowded and sinuous. At an early 
period the tip of the fetal sac in each cornu becomes necrotic and 
either extends forward toward the oviduct as a naked, flattened, 
yellow, hard cord, incrusted in a calcareous-like substance, or it 
becomes invaginated into the cavity of the amnion or allantois. In 
the gravid horn the necrotic tip is generally invaginated into the fetal 
sac, while in the nongravid horn it largely lies naked, 1 to 6 or more 
inches long, lying free in the apex of the horn. 
When the necrotic tip is naked and exposed, when it comes in con- 
tact with the cornual mucosa, it is generally surrounded by a finely 
granular, yellowish or dirty lemon-colored fluid, suggesting a suspen- 
sion of pale yellow brick dust in a fluid. There may be but a few 
drops, or the amount may reach 1, 2, or even 5 to 10 ounces. It 
appears like an exudate resulting from the mechanical irritation of the 
exposed necrotic tip and tends to be large or small in volume, accord- 
ing to the size of the necrotic tip. 
While these necrotic tips are universal at the cornual apices, there 
appears rarely a very similar phenomenon at the internal os. Appar- 
ently in the few instances observed the fetal sac had pushed out for a 
distance through the internal os, and, like the projections into the 
apices of the horns, became necrotic, and was later surrounded by the 
pale, brick-dust sediment. 
PREVALENCE OF ABORTION, 
The history of contagious abortion of cows is extensive, though it 
loses much of its interest and definiteness because of the inadequacy 
of the means for its diagnosis. 
Abortion statistics in any herd are necessarily inaccurate, and 
include only those cases in which the fetus has perished and been 
expelled at a period when its death and expulsion is recognized. In 
many outbreaks of abortion there is associated a large amount of 
sterility. Many of these instances of assumed sterility are in reality 
