NERVOUS SYSTEM. 123 



240. Glands. 



A gland is an organ composed of blood-vessels, nerves and absorbents, 

 and destined for the secretion or alteration of some particular fluid, as 

 for instance the salivary glands secrete saliva, the lachrymal glands tears, 

 and the sebaceous glands oil. 



Secretions are divided into two classes, technically termed recrementi- 

 tious and excrementitious. The former are those, which after being 

 separated and secreted are returned again to the blood for further employ- 

 ment in the animal economy. The latter are those, which are cast off as 

 superfluous and incapable of administering to nutrition, such for instance 

 as the urine, perspiration, &o. 



Glands are infinite in variety as to size, shape and physical appearance. 

 They all have absorbent vessels. When the secretion of a gland is veiy 

 large, as in the kidneys and liver, its blood-vessels are also very large. 

 All glands secrete from arterial blood, except the liver, which is able to 

 secrete from both venous and arterial blood. The blood in its passage 

 through a gland is retarded by means of the convolutions of the capil- 

 laries about the minute ends of its ducts, and hence time is griven for the 

 process of secretion. 



As the circulation in a gland is increased, so is its secretion. Thus in 

 the first stage of inflammation a gland secretes more, because the circu- 

 lation is increased ; whilst in the latter stages, when the circulation is 

 stagnant, the secretion decreases. Again in health we easily recognise 

 the effect of strong exercise and consequent increased activity of the cir- 

 culation in the greater secretion poured forth by the perspiratory glands. 

 • The nimiber of very different secretions made by the glands from the 

 blood must excite our wonder and admiration. How different, for in- 

 stance, are serum, m'ine, bile, and saliva. Each gland performs its 

 office in a mysterious manner, elaborating principles which exist in a 

 latent state in the blood. 



CHAPTER U. 



THE NERVOUS SYSTEM. 



241. Plan of tlie nervous sij stem. 242. 'ihe Nerves. 243. Functions of 

 the nsrvous system. 244. Influence of the nervous system in reference to 

 disease. 245. Medicines acting on the nervous system. 



241. Plan of the nervous system. 



I 



^m According to Bichat the Nervous system may be separated into two 

 ^m great divisions. The first or Cerebro-spinal system includes the brain 

 ^B and spinal cord and the nerves connected with them and their ganglia. 



