THE CYCLIC CHANGES IN THE OVARY OF THE 
GUINEA PIG 
LEO LOEB 
From the Laboratory of Experimental Pathology of the University of Pennsylvania, 
and from the Pathological Laboratory of the Barnard Skin and Cancer Hospital, 
St. Louis, Mo. 
In the course of an experimental investigation into the causes 
of the cyclic changes taking place in the uterine mucosa and into 
the factors underlying the formation of the maternal placenta in 
mammals, we observed that cyclic changes in the structure of 
the ovary correspond to the uterine cycle. It has of course been 
known that at certain times ovulation takes place in the mamma- 
lian ovary, and furthermore, changes have been described as occur- 
ring in the ovarian follicles of certain mammals in connection 
with copulation and during pregnancy; but the cyclic changes 
taking place in the ovary quite independently of copulation 
and of pregnancy and merely dependent upon ovulation have, 
as far as we are aware, not yet been recognized. While 
we know of no publication dealing with the cyclic changes 
in the ovaries in general, a valuable study of the changes taking 
place during pregnancy in two species of Insectivores and in one 
species of Lemurid has been made by C. H. Stratz.1. This author 
comes to the conclusion that in the period following copulation 
all the ovarian follicles become atretic; that during pregnancy 
small follicles are formed but also become atretic before they can 
develop; that only towards the end of pregnancy the follicles 
begin to grow to a considerable size, and that they reach the stage 
of maturity during the puerperium. 
Stratz was not in a position to determine in an exact manner 
the time elapsed since the last copulation of the animals the ova- 
1C. H. Stratz: der geschlechtsreife Siugethiereierstock. Haag. 1898. 
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