LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE 29 



A further instance of nerve-regulation is seen in secreting glands. Not 

 all glands are thus regulated, at least not directly ; but in those which are, 



the effects are striking. Their regulation is of the same 

 Regulation of general nature as that exercised upon involuntary 



muscle, but it influences the chemical activities of the 

 gland-cells and the outpouring of secretion from them. 

 By means of this regulation a secretion can be produced or arrested, 

 increased or diminished. As with muscle, a suitable balance is in this 

 way maintained, and the activity of the glands is adapted to the require- 

 ments of the organism. Most of the digestive glands are thus influenced, 

 as are the skin-glands which secrete sweat. And by the action of the 



nervous system upon the skin-glands, together with its 

 effect in increasing or diminishing the blood-supply to 

 the cutaneous blood-vessels, the temperature of our 

 blood is regulated and is kept at the point best suited for maintenance of 

 the life and activity of the tissues. 



The action of the nervous system upon the secretion of glands is 

 strikingly exemplified, as in the case of its action upon the heart and 



blood-vessels by the effects of the emotions. Thus an 

 emotion of one kind such as the anticipation of food- 

 will cause saliva to flow ' the mouth to water ' ; 

 whereas an emotion of another kind such as fear or anxiety will stop 

 the secretion, causing the 'tongue to cleave unto the roof of the mouth,' 

 and rendering speech difficult or impossible. Such arrest of the salivary 

 secretion also makes the swallowing of dry food difficult : advantage of 

 this fact is taken in the ' ordeal by rice ' which used to be employed in the 

 East for the detection of criminals. 



The activities of the cells constituting our bodies are controlled, as 

 already mentioned, in another way than through the nervous system, 



viz., by chemical agents (hormones) circulating in the 



f*. m , * * V ^J * *-J 



chemical^ gents : blood. Many of these are produced by special glandular 

 hormones, internal organs, known as internally secreting glands. The 

 secretions. ordinary secreting glands pour their secretions on the 



exterior of the body or on a surface communicating with the exterior ; the 

 internally secreting glands pass the materials which they produce directly 

 into the blood. In this fluid the hormones are carried to distant organs. 

 Their influence upon an organ may be essential to the proper performance 

 of its functions or may be merely ancillary to it. In the former case 

 removal of the internally secreting gland which produces the hormone, or 

 its destruction by disease, may prove fatal to the organism. This is the 



case with the suprarenal capsules : small glands which 

 Suprarenals. are a( jj acen t to t h e kidneys, although having no 



physiological connection with these organs. A Guy's physician, Dr. 

 Addison, in the middle of the last century showed that a certain affection, 

 almost always fatal, since known by his name, is associated with disease 



