Cole and Goss loq 



mare 2, selected for study, is much smaller than those selected from the other 

 mares, it is likely that this case represents an earlier stage. Cups of various sizes 

 are found side by side at this stage of pregnancy. We saved a minimum of mate- 

 rial for histological study because of our interest in hormonal concentration. 



This development of the interglandular tissue is comparable to the decidual 

 responses of the endometrium during pregnancy in other forms. Plate 1, figure 

 1, gives evidence, in truth, that the superficial part of the cup is sloughed, as the 

 outline of the cellular debris is still evident. This sloughing begins early in 

 pregnancy, as plate 2, figure 6, shows; the epithelium of the mucosa is already 

 completely lost. In plate 1, figure 2, the uterine epithehum is still intact at the 

 lips of the cup but completely lacking in the central portion. Perhaps one is 

 justified in referring to this as a decidual response, even though the tissue is 

 shed prior to parturition. 



Plate 1, figure 1, shows the pendulous character which the cups assume at 

 the 105th day of pregnancy. These bodies extending into the allantoic cavity 

 are, no doubt, an early stage of the pendulous hippomanes. 



Concentration of Gonadotrophin in Endometrial Cups and 

 Other Selected Tissues of the Mare 



Preparation and Assay of Tissue Extracts. Only a small amount (37 mg.) of 

 endometrial secretion was taken for assay from the endometrial cups of mare i . 

 This was dried in a vacuum desiccator, again weighed, and then taken up in 

 10 cc. of sterile saline for assay. This secretion was found to contain 29.5 per 

 cent solids. The amount of secretion in this mare was very small. We did not, 

 however, attempt to remove it quantitatively, for we did not know of its im- 

 usual activity prior to this time. The endometrial secretion in mares 2, 3, 

 and 4 was much more abundant. These thick mucus-secretions were carefully 

 scraped from the cups and weighed, then taken up in either 100 or 200 cc. of 

 sterile saline, forming a uniform opalescent solution. A small aliquot was 

 removed from each solution for assay and the remainder frozen at once. 



The endometrial cups, the endometrium between the cups, and the chorion 

 were weighed and ground with sand under sterile saline. The mixture was 

 centrifuged and the residue reground and extracted as before. This process 

 was repeated three or four times and the extracts combined. The volume of 

 the extract was noted, a sample removed for assay, and the remainder frozen. 



The pituitary was extracted by repeated giinding with sand and 2 per cent 

 pyridine solution, separating the extract by centrifuge (Fevold^ suggested using 

 2 per cent pyridine for extraction of pituitary tissue). To the combined extracts 

 were added 6 volumes of 100 per cent acetone. The precipitated material, after 

 standing at 2° C. over night, was removed by centrifuging, and taken up in 

 20 cc. of sterile saline for assay. 



The tissues, with the exception of the pituitaries, were assayed by the method 

 of Cole and Erway.^ The pituitary extracts were assayed by the weight method 

 of Cole and Saunders" suggested for mare serum, with the exception that the 



