4 o6 VETEEINAEY PHYSIOLOGY 



urine. This is best marked when the animal is well fed and 

 has a store of glycogen in its liver, but since it occurs in fasting 

 animals, after the stored carbohydrates have been cleared out 

 by the administration of phloridzin (p. 385), 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 proteins. 

 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 prevent- 

 ing the formation of the internal secretion which has been 

 supposed to act on the liver (see p. 410). But the evidence 

 is not satisfactory. 



Its continued administration produces atheroma of the aorta. 



The essential principle of the suprarenals is a substance, 



adrenalin, which is of the nature of a secondary alcohol linked 



to a benzene ring. Various more or less successful attempts 



have been made to prepare it synthetically. 



The functions of the cortex of the suprarenals are unknown. 

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

 and consists of an anterior part of nervous tissue, somewhat 

 resembling the medulla of the suprarenals, and a posterior part 

 derived from the alimentary canal, and consisting of masses of 

 epithelial-like cells. 



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

 temperature^ lassitude, muscular twitchings, dyspnoea, 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 a rise of arterial blood pressure, a dilatation of 

 the kidney, and an increased flow of urine. A repetition of the 

 injection may cause a fall of blood pressure, but the dilatation 

 of the kidney and the increased flow of urine are produced. 



3. Thyroid Gland (fig. 164). 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-protein, and 



