THE DUCTLESS GLANDS. 325 



secretion must be still regarded as somewhat obscure. In part, 

 it exerts its influence by increasing or diminishing the quantity 

 of blood supplied to the secreting gland, in virtue of the power 

 which it exercises over the contractility of the smaller blood- 

 vessels ; while it also has a more direct influence analogous to 

 the trophic influence referred to in the chapter on Nutrition. 

 Its influence over secretion, as well as over other functions of 

 the body, may be excited by causes acting directly upon the 

 nervous centres, upon the nerves going to the secreting organ, 

 or upon the nerves of other parts. In the latter case, a reflex 

 action is produced : thus the impression produced upon the 

 nervous centres by the contact of food in the mouth, is reflected 

 upon the nerves supplying the salivary glands, and produces, 

 through these, a more abundant secretion of saliva. 



Through the nerves, various conditions of the mind also in- 

 fluence the secretions. Thus, the thought of food may be suf- 

 ficient to excite an abundant flow of saliva. And, probably, 

 it is the mental state which excites the abundant secretion of 

 urine in hysterical paroxysms, as well as the perspirations and, 

 occasionally, diarrhoea, which ensue under the influence of 

 terror, and the tears excited by sorrow or excess of joy. The 

 quality of a secretion may also be affected by the mind ; as in 

 the cases in which, through grief or passion, the secretion of 

 milk is altered, and is sometimes so changed as to produce 

 irritation in the alimentary canal of the child, or even death 

 (Carpenter). 



The secretions of some of the glands seem to bear a certain 

 relation or antagonism to each other, by which an increased 

 activity of one is usually followed by diminished activity of 

 one or more of the others ; and a deranged condition of one is 

 apt to entail a disordered state in the others. Such relations 

 appear to exist among the various mucous membranes : and 

 the close relation between the secretion of the kidney and that 

 of the skin is a subject of constant observation. 



CHAPTER XIII. 



THE VASCULAR GLANDS; OR GLANDS WITHOUT DUCTS. 



THE materials separated from the blood by the ordinary 

 process of secretion by glands, are always discharged from the 

 organ in which they are formed, and either straightway ex- 



28 



