396 Messrs. F. H. A. Marshall and W. A. Jolly. [May 13, 
The second period is characterised by congestion and increase in the number 
of capillaries. This is followed in the next period by extravasation of blood 
and emigration of polymorphs. External bleeding is shortly afterwards 
observed, having been preceded by a flow of mucus, containing polymorphs. 
There is considerable denudation of uterine epithelium, but the denudation 
does not extend to nore than a single layer of stroma cells. In the recupera- 
tion period the epithelium is re-formed and new capillaries arise. This stage 
is also characterised by the large number of leucocytes that occur free in 
the stroma. These are of several kinds: (1) Large mononuclear leucocytes 
containing iron pigment derived from the extravasated red corpuscles, 
(2) coarsely granular eosinophil leucocytes, and (3) basophil cells. The 
latter, which occur in unusual abundance both in the stroma and in the 
muscle layers, are often very large. It is obvious that the changes occurring 
in the uterus throughout the cycle are homologous with those which are 
undergone in the sheep, the ferret, the monkey, and the human female. 
Ovulation and the Vitality of the Spermatozoa.—Ovulation in the bitch 
takes place after external bleeding has been going on for several days. It 
occurs during the period of cestrus but it is quite independent of coition or 
of the presence of spermatozoa in the uterus. 
No systematic investigation as to the vitality of mammalian sperms has 
hitherto been attempted. It has been ascertained by us, however, that the 
period of survival in the male passages of rabbits is probably not more than 
10 days. 
Some Theoretical Considerations—The fact that ovulation does not take 
place until after the procestrum (or at any rate until after the commencement 
of the external bleeding stage of the procestrum) is in opposition to the view 
that heat and menstruation are produced by ovulation, or by the corpus 
luteum. It is also contrary to the theory that the degeneration stage occurs 
as a result of the absence of a fertilised ovum for which the preceding growth 
was preparing. The theory that the destruction stage of the procestrum is 
of the nature of an abortion related to an ovum released at the preceding 
period is untenable, owing to the comparative infrequency of the heat periods 
(and, therefore, of the ovulation periods) in the bitch. On the other 
hand, the hypothesis that the entire procestrous process is of the nature 
of a preparation for the lodgment of the ovum is in accordance with the facts. 
Part II. 
The Cause of Heat—As pointed out by Brown-Séquard and others, the 
ovaries, like the testes, exercise an influence on the general metabolism of the 
organism throughout the reproductive period. Ovarian medication has been 
