THE DUCTLESS GLANDS 1233 



condition for the carrying out of the normal functions either of growth 

 or activity of many other parts of the body. In other cases an organ may 

 have a twofold function. Thus the pancreas gives an external secretion 

 which is used for the preparation of the food for absorption, and an internal 

 secretion which, passing into the blood, exercises an important influence on 

 the metabolism of the foodstuffs after absorption. Other instances of 

 these chemical correlations may be cited. The secretion of gastric juice, 

 which results from the presence of peptones or other substances in the 

 stomach, has been ascribed by Edkins to the production in the pyloric 

 mucous membrane of a gastric hormone, which travels by the blood to the 

 glands of the fundus, where it excites secretion of gastric juice. According 

 to Frouin the injection of boiled succus entericus, free from secretin, provokes 

 the secretion of intestinal juice. In the reproductive system we have 

 many examples of such chemical correlations. The pancreas, by its internal 

 secretion, probably influences not only the oxidation of the carbohydrates 

 but also the assimilation of the foodstuffs by all parts of the small intestine. 

 All these examples are discussed in fuller detail in other parts of this .book. 

 There is one class of organs in which a chemical influence exerted on the 

 rest of the body is the only function with which we are acquainted. These 

 are included under the term ductless glands. As examples, we may cite the 

 suprarenal bodies, the thyroid and parathyroids, the thynms and the 

 pituitary body. 



THE SUPRARENAL BODIES 



The suprarenal capsules in mammals are two small masses lying on the upper or oral 

 side of the kidneys. They consist of two parts, the cortex and the medulla. The 

 cortex is composed of cells arranged in columns or in a reticular fashion. The outermost 

 layer of cells often presents an alve'6lar structure, the lumen however being but little 

 marked. According to the arrangement of the cells the cortex is divided into three 

 zones, the zona glomerulosa, zona fasciculata, and zona reticulata. The cells them- 

 selves are distinguished by the large amount of granules they contain, which give 

 the ordinary reactions for fat but consist probably of lecithin compounds. In some 

 animals e. g. the guinea-pig, the cells, especially towards the inner part of the gland, 

 contain many yellow pigment granules. The medulla, much less extensive than the 

 cortex, presents irregularly shaped cells, the outlines of which are but slightly marked. 

 These cells contain granules which stain darkly with chromates and give a green colour 

 with salts of iron. It is hence easy to delimit the area of the cortex in any section of a 

 gland which has been hardened in a fluid containing chromates. The substance giving 

 this reaction is known as chromophile or chromaffine substance. The suprarenals are 

 richly supplied with blood, especially in the medullary part, the cells of which impinge 

 directly on the endothelial lining of dilated capillaries. They also receive an abundant 

 nerve supply from the sympathetic system, the nerves forming a thick meshwork, 

 especially in the medulla, and presenting at intervals ganglion cells which may be 

 isolated or combined to form small ganglia. 



A study of the development of the suprarenal glands shows that we have here to do 

 with two distinct tissues, probably differing in the part th'jy play in the animal economy. 

 Whereas the cortex is derived from that portion of the mesobiast, the * intermediate 

 cell mass,' from which the mesonephros is also developed, the medulla is produced 

 by an outgrowth from the sympathetic system and may be said indeed to consist of 

 profoundly modified nerve cells. In many fishes these two elements of the suprarenal 

 gland remain separated throughout life, the cortex being represented by a series of 

 7B 



