V - The secretory phenomena in the oviduct of the fowl, including the process of shell formation examined by the microincineration technique

The present studies were commenced primarily to investigate the cytological phenomena in glandular tissues in which the secretion consists mainly of inorganic salts in solution. In selecting convenient material, the fowl uterus was chosen as a vertebrate organ liberating a secretion which, in view of the chemical composition of the egg shell, must contain calcium salts in high concentration with a trace of magnesium carbonate, but without significant amounts of iron, silicon, or aluminium. From previous investigations, it has been established that at least two types of gland cells exist in the lining epithelium of the uterus and that of the tubular glands of the uterine corium, both of which contribute to the final stages of egg-shell formation in the fowl. The addition of half the total egg-white, in the form of thin fluid albumen, has been conclusively attributed to the activity of the uterine glands, but no convincing localization of the egg-shell secretion has been made owing to the remarkably low concentration of calcium salts in the actively secreting uterus ; a concentration for which the ordinary histo-chemical tests are ineffective. The technique of microincineration, which hitherto has been confined largely to problems of a histological or embryological nature, owing to the difficulty of obtaining delicate cytological detail in the ash residues, was examined as a possible means of identifying the storage and elaboration of inorganic material in the uterine gland cells and its later extrusion as the mature secretion. A comparative examination of the mineral content of regions adjacent to the uterus and the cytology of heavy albumen secretion in the cranial sections of the oviduct, led finally to a study of secretory processes in the entire organ. The more important phases of the glandular activity in the infundibulum, albumen region, and the isthmus have been reinvestigated, particularly where lack of agreement exists, in recent literature, on details of major importance. A final solution, however, of many aspects of this problem naturally rests on the histo-chemical analysis of material fixed and sectioned without the use of protein precipitants or solvents. In this connection the new freezing-drying technique of Gersh (1932) might prove to be most suitable.