THE DUCTLESS GLANDS 1181 



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 food-stuffs 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 food-stuffs 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 thymus 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 alveolar 

 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 themselves 

 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 sym- 

 pathetic 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. 



