880 PHYSIOLOGY OF DIGESTION AND SECRETION. 



menters, who have studied carefully the effects of partial or com- 

 plete removal of the adrenals in mammals, record their opinion that 

 it is the cortex rather than the medulla that is essential to life.* 

 The nature of the secretion furnished by the cortex and its normal 

 functional value are matters of speculation only at present. 

 Chemical examination of the cortex shows the presence of much 

 lipoid material, particularly of the cholesterin esters, and it may be 

 that through this material the tissue influences the metabolism in 

 other parts of the body. 



Observers have also called attention repeatedly to the fact that 

 the cortex has some relation to the activity of the sexual glands. 

 During pregnancy the cortex undergoes hypertrophy, and in some 

 cases pathological changes affecting the cortex alone have been fol- 

 lowed by precocious development of the sexual organs. On the 

 other side, castration causes changes in the adrenal bodies and, 

 indeed, the various phases of sexual life are accompanied by histo- 

 logical changes in the adrenals. But others of the glands of inter- 

 nal secretion have some similar functional relation with the repro- 

 ductive glands or their contained interstitial tissue, and no specific 

 suggestion can be offered at present in regard to the particular part 

 taken by the adrenal cortex. | 



Pituitary Body (Hypophysis). This body is usually described 

 as consisting of two parts a large anterior lobe of distinct glandu- 

 lar structure and a much smaller posterior lobe of nervous origin 

 and composed chiefly of neuroglia cells and fibers. Embryologic- 

 ally the two lobes are entirely distinct. The anterior lobe arises 

 from an invagination (Rathke's pouch) of the buccal ectoderm. A 

 portion of this epithelium soon develops into a glandular structure, 

 belonging to the type of glands which have no excretory duct and 

 which probably, therefore, form an internal secretion. The pos- 

 terior lobe arises as an outgrowth from the floor of the third ven- 

 tricle of the brain, the infundibulum, which comes into contact 

 with the epithelial pouch forming the anterior lobe. The epithelial 

 cells of the latter soon show a differentiation into two parts, one of 

 which gives rise to the anterior lobe, while the other invests the 

 body and neck of the posterior or nervous lobe. To this latter the 

 special name of the pars intermedia has been given. When fully 

 formed the posterior lobe consists of two parts, the pars nervosa, 

 composed of neuroglia cells and fibers and ependymal cells, and an 

 investing layer of epithelial cells, derived from the buccal ectoderm 

 and known as the pars intermedia (see Fig. 299). 



* Crowe and Wislocki, "Johns Hopkins Hospital Bulletin," October, 1914. 



f For details and references to literature on this and other points in inter- 

 nal secretion consult the excellent work by Biedl, "Innere Sekretion," Berlin, 

 1913. 



