164 DELLA DRIPS 
of pregnancy and that regressive changes do not begin until the 
period of pregnancy is over. Miller says there is no neutral fat 
in the human corpus luteum until regression sets in at birth. 
Because the first-mentioned group of men found that double 
ovariectomy did not cause abortion in rabbits after the fifteenth 
day, and did so earlier than this, they considered this lipoid 
secretion related to changes in the uterus occurring between the 
fourth and fifteenth days after coitus, or between the time of 
the fixation of the blastocyst and the middle of the period of 
pregnancy. 
Van der Stricht seems to have been the first to conceive of the 
presence of a secretion in the luteal cells prior to the appearance 
of the lipoid droplets which coexists with them for some time 
after their appearance. He judges of the presence of this 
secretion in the cells from its presence in the near-by inter- 
cellular spaces and lymphatics. The latter, according to van 
der Stricht, are the avenues of excretion of both the serous and 
the lipoid secretions. 
In spermophiles, the lipoid product does not begin to appear 
in the luteal cells until the period of pregnancy is half over and 
is not very abundant until after birth. As far as these animals 
are concerned, then, the lipoid product is not the active sub- 
stance of the corpus luteum which has specific effects on the 
uterus during pregnancy. This active substance is rather a 
secretion represented in the cells by the secretory granules 
previously noted, which are of a very different nature from the 
lipoid droplets. 
The second internal secretion which is Rea eee in the 
luteal cells by lipoid droplets and which formerly has been 
considered the secretion which is responsible for the changes 
occurring in the uterus incident to pregnancy, must be con- 
sidered, as far as the spermophiles are concerned at least, as 
having another function. There seems to be some relationship 
in these animals between the period of greatest abundance of 
the lipoid product in the cells and the period of regression and 
atrophy in the uterus. The uterus of the spermophile atrophies 
very slowly, much more so than in animals that bear several 
