THE MENSTRUAL CYCLE 



up into tiny capillary vessels (not shown in the diagram) 

 that supply the inner one-third of the endometrium. The 

 other kind of branching is that of the straight arteries, which 

 run a short course directly to supply the basal two-thirds 

 of the endometrium. 



By studying under his microscope a series of uteri of 

 women and monkeys, collected at successive stages of the 

 cycle, Bartelmez showed that the fundamental step in the 

 menstrual breakdown is a shut-off of the coiled arteries. 

 With such material, however, it is possible to see only in- 

 terrupted stages of the process ; the sequence cannot be seen 

 in full. Markee has therefore made use of a remarkably 

 clever means of watching menstruation in progress.^ Since 

 we cannot see into the uterus, he undertook to put that organ 

 (or rather, small pieces of its lining) into a situation where 

 it can be watched. He grafted bits of endometrium into the 

 anterior chamber of the same animal's eye, thus applying a 

 method already used by a few investigators for other pur- 

 poses. The small grafts are placed just behind the clear 

 cornea, and get their blood supply through vessels which 

 grow into them from the iris. The operation of grafting, 

 which is done under complete anesthesia, is relatively simple, 

 though, of course, it requires deft hands. The animal suffers 

 no discomfort from the graft and is inconvenienced only by 

 the fact that while under observation she has to sit in a 

 tight wooden box, something like a pillory (but more com- 

 fortable), while the investigator studies her eye through 

 a microscope. He is, by the way, at least as uncomfortable as 

 the monkey, because the task of watching the winking, rov- 

 ing eye of the animal, changing the focus and moving the 

 microscope and light whenever necessary, is enough to ex- 

 haust the patience even of a scientist. 



5 J. E. Markee, "Menstruation in intraocular endometrial transplants 

 in the Rhesus monkey." Carnegie Institution of Washington, Publication 

 No. 518 {^Contributions to Embryology, vol. 28), pp. 219-308, 1940. 



{ 151 } 



