Period of Heat 193 
brane, and dies. Opening into the vagina at its lower 
surface, close to the vulva, is a small tube, the urethra, 
whien connects with the bladder, and through which 
the urine is discharged. This is mentioned particularly 
because, in passing probes or other small instruments 
into the vagina, they should be directed toward the 
upper part of the vagina, to avoid passing them through 
the urethra into the bladder. 
When an ovum, or egg, is discharged from an ovary 
into the fallopian tube, it is attended by certain symp- 
toms of nervous or sexual excitement, and an abnormal 
discharge of mucus from the vagina. To this period, 
the term “heat” or “rutting” is commonly applied 
by stockmen.’ During this period, the female is desirous 
of sexual intercourse. If intercourse takes place and 
conditions are favorable, the ovum or egg is fertilized 
by the male cell and, instead of passing out and dying, 
remains in the uterus, to the wall of which it becomes 
attached. It develops into a young animal of the same 
species, except when animals of different species are 
crossed, in which rare instances a hybrid is the result. 
as, for example, the mule. The period of heat varies in 
different animals, about as follows: 
Mare, once in three weeks, and lasts from two to three days. 
Cow, once in three weeks, and lasts from fifteen to thirty hours. 
Ewe, once in sixteen days, and lasts two to three days. 
Sow, once in two to three weeks, and lasts one to three days. 
Bitch, once in four to six months, and lasts nine to fourteen days. 
These dates refer to the average time that elapses from 
one period of heat to another, providing pregnancy 
does not occur. 
M 
