364 EMBRYOLOGY 



Condition of Ovary as Index to Pregnancy. On opening the 

 body cavity of a mammal, first of all examine the ovary. By 

 so doing one can estimate roughly the time that has elapsed 

 since the discharge of the ovum or ova. Prominent stigmata 

 or areas with a blood-clot centre indicate recent ovulation 

 while a smooth surface of yellowish appearance indicates a corpus 

 luteum, which means that some time has elapsed since ovulation. 



802. Isolation of the Eggs and Early Stages.* The tubae and 

 uterus or uteri are dissected out and treated in one of two ways : 

 either the isolated tuba after straightening is washed out from the 

 funnel opening with warm salt solution, or with some fixative like 

 formalin or weak osmic acid, or on the other hand the whole 

 length of the tube is laid open and spread out with a scalpel or 

 sharp scissors and needles, and the eggs are looked for under a 

 dissecting microscope. 



If the method of washing out is adopted, it is best to use a good 

 rubber bulb attached to a glass tube which has been drawn out 

 finely enough to pass into the oviducal opening. Kolliker used 

 Miiller solution or weak osmic acid for injection, collecting the 

 fluid in a series of watch-glasses ; J. P. Hill uses solid crystal 

 dishes, which can easily be examined under a stereoscopic binocular 

 microscope. As a fluid for washing out Hill's picronitric osmic 

 {vide infra), weak formalin, or weak osmic acid are probably as 

 good as anything. The success of this injection method depends 

 on the amount of mucus in the tuba and on the condition of the 

 folds in its mucosa ; if the eggs are not found after the injection, 

 the walls of the tube may be opened up with scissors and the 

 lining scraped away with a small scalpel ; the mucus thus procured 

 may be diluted with a little indifferent fluid and examined on a 

 slide under the microscope. Both operations of injection or of 

 opening the tuba may succeed with comparatively large animals 

 like the rabbit and dog. It is practically impossible to slit open 

 the tuba of the cat. 



In cases where the subject is small, as, for instance, the mouse, 

 it is necessary to preserve the whole oviduct and use a fixative 

 sufficiently penetrative to act quickly. Even with the guinea-pig 

 the lumen of the tube is so small that it is difficult to remove the 

 ova ; we consider that attempts to press out the contents of the 

 tubes are dangerous. In such cases it seems better to cut the tube 

 into lengths with a razor and to fix whole {vide infra). Bischoff 

 in his study on the guinea-pig (Giesson, 1852), and Ballowitz 

 {Arch. Anat. Physiol., 1883) both resorted to the method of 

 squeezing out the contents of the tubes. 



When found the ova are picked up with the point of a cataract 

 needle or a scalpel, on a piece of black paper cut to a point, or 

 with a pipette, and either examined fresh in the peritoneal fluid 

 * See Allen and co-workers, Contrib. Embryol. Carncg. Inst. Wash. 1934. 



