386 HUMAN PHYSIOLOGY 



have been cleared out by the administration of phloridzin 

 (p. 368), it would appear to be due, in part at least, either 

 to a non-utilisation of sugar by the tissues or to an increased 

 production of sugar from proteids. A decrease in the nitrogen 

 in the form of urea and an increase of that in ammonia, 

 similar to that found in cases of true diabetes, have also 

 been observed. 



It has been suggested that the suprarenal secretion acts 

 through the pancreas by preventing the formation of the 

 internal secretion which has been supposed to act on the 

 liver (see p. 390). But in birds it acts even after removal 

 of the pancreas. 



The essential principle of the suprarenals is a substance, 

 adrenalin, the constitution of which is now known. Various 

 more or less successful attempts have been made to prepare 

 it synthetically. 



2. Pituitary Body. This lies at the base of the mid- 

 brain, and consists of a posterior part of nervous tissue, 

 somewhat resembling the medulla of the suprarenals, and 

 an anterior part derived from the alimentary canal, and 

 consisting of masses of epithelial-like cells. 



Removal of this body causes in cats and dogs a fall of 

 temperature, lassitude, muscular twitchings, dyspmjea, and 

 ultimately death. Injection of extracts of the substance is 

 said to diminish these symptoms. In the healthy animal 

 the injection of extracts of the posterior or nerve parts of 

 the pituitary causes an augmentation of the force of cardiac 

 contraction, and a contraction of the arterioles, and thus 

 raises the arterial pressure. 



3. Thyroid Gland (Fig. 152). This structure is formed as a 

 hollow outgrowth for the anterior part of the alimentary canal, 

 which branches and again branches. It early loses its con- 

 nection with the alimentary canal, and becomes cut up by 

 fibrous tissue into a number of small more or less rounded 

 cysts or follicles, each lined with epithelium, and filled with 

 a mucus-like substance, which contains a nucleo-proteid, and 

 a substance with a marked power of combining with iodine. 

 This has been called lodothyrin. It contains about 3'6 per 

 cent, of iodine, and it seems to be the active constituents of 

 the internal secretion of the gland. 



