92 THE BODY AT WORK 



very large larger at one period than the kidney. At this 

 period bloodvessels are formed in them with great rapidity 

 by a curious process of boring through and channelling out of 

 their cells. There are other facts connected with their develop- 

 ment in the individual and their varying form in different classes 

 of Vertebrate animals which point to a " previous existence," 

 but there is nothing to indicate that they were ever open 

 glands. In all vertebrates they are closed masses of cells, the 

 only function of which, so far as we know, is to produce an 

 internal secretion ; but the importance of this chemical mes- 

 senger in bringing about the proper working of other organs is 

 almost startlingly evidenced by the collapse which follows dis- 

 ease, or removal of the organ which produces it. 



The suprarenal capsules yield a substance which has been 

 termed " adrenalin." It contains nitrogen, is crystallizable 

 and dialysable ; but its chemical relationships have not been 

 made out as yet. It is not destroyed by boiling, nor by diges- 

 tion with gastric juice. Injected into a vein, it causes, amongst 

 other effects, an immense rise in blood-pressure, even though 

 the amount injected be extraordinarily small. Applied locally 

 as a wash or spray, a solution of 1 part in 10,000 pro- 

 duces marked blanching of the surface ; and it is useful, in 

 consequence, as a means of checking bleeding in small opera- 

 tions, especially those on the eye or the nose. It is a most 

 energetic poison. Even J milligramme is sufficient to kill 

 a rabbit. In short, adrenalin acts like the most powerful 

 drugs known to physicians ; and this drug, manufactured by 

 the suprarenal capsules, is constantly added to the blood. 

 Disastrous consequences follow a failure in the regular supply. 



The tone of the vascular system is maintained by adrenalin. 

 The nature of its influence upon muscles is not known, but prob- 

 ably the complete loss of muscular strength, which is one of the 

 most noticeable symptoms of disease of the suprarenal capsules, 

 is an indirect result of the lowering of blood-pressure. The 

 muscles, it must be remembered, make up about one-third of 

 the weight of the body of a muscular man. For the exchange 

 of their waste products for food, they are dependent upon an 

 efficient circulation. They are unable to display their normal 

 vigour when the vascular system is not up to its work. 



The Pituitary Body is another ductless gland of dubious 



