OF GLANDS. 167 



those of older ; and from the alteration which takes place 

 in the kidney and thymus gland, we see that some change 

 really does take place in their size during life. The 

 nerves of glands are small, and their sensibility is not con- 

 siderable. 



Glands have absorbents, which in some instances, as 

 those of the liver, are very large. Their bloodvessels, 

 both arteries and veins, are usually of a proportionate size ; 

 but the magnitude of the vessels is increased when the 

 amount of secretion is considerable, as in the kidneys. In 

 its passage through glandular bodies, the blood is found to 

 be retarded by means of the capillaries being convoluted 

 around the minute ends of the ducts. All glands secrete 

 from the arterial blood, except the liver, which separates the 

 bile from venous blood. Among the phenomena that these 

 bodies present, a sympathetic property is a marked one. 

 The sight of food stimulates the salivary glands. The 

 sympathy of the kidneys with the skin is very considerable ; 

 and, when either becomes greatly excited, the secretion of 

 the other diminishes. In summer, when the skin is in full 

 action, and the blood pours out its aqueous particles 

 in great plenty, little urine is made ; but in winter the 

 reverse takes place. As the circulation through a gland is 

 increased, so is the secretion enlarged likewise ; hence under 

 the first stages of inflammation glands secrete more, because 

 the circulation is quickened ; but in the latter stages of it, 

 and when the circulation becomes almost stagnant, the 

 secretion is lessened, or totally stopped. The individual 

 glands will be described with the parts to which they more 

 immediately belong. 



The physiology of secretion is but little known. Those 

 procured from one liquid (the blood) are so different ; as 

 urine, semen, bile, saliva, &c., that their evident distinctions 

 cannot fail to excite our wonder and stimulate our inquiries. 

 Glandular secretion has been supposed to depend on the 

 previous existence of the secreted matter within the blood, 

 and the glands only to separate these component par- 

 ticles. But the blood, it has been answered, possesses 

 the same chemical properties throughout the body ; and 

 drawn from whatever secreting organ it may be, it is the 

 same. Nevertheless, the elementary principles of all these 



