Action of Glands. 519 



contraction reduces the size of the tube and thus causes increased blood 

 pressure. Under these circumstances the heart is made more active, 

 the pressure probably forcing more blood into the heart muscles through 

 the coronary arteries, and thus stimulating and at the same time sup- 

 plying them with greater power. 



CHAPTER LIY. 



ACTION OF GLANDS, 



The glands are similar to the muscles in many respects though their 

 structure is different. ' ' A gland of the simplest form is a cavity lined 

 with cells opening by a longer er shorter passage through the outer 

 surface of the mucous membrane or the outer skin (corium), which 

 lies above it. The cavity may be hemispherical, flask shaped, or tubular. 

 In the latter case the tube is often very long, and is either wound like a 

 thread or is coiled and is sometimes expanded at its closed end in the 

 form of a knob. These are all simple glands. Compound glands are 

 found when several tubular or knob-shaped glands open with a common 

 mouth. " ( Rosenthal. } 



These glands are variously occupied in secreting from the blood vari- 

 ous substances sweat, fat, saliva, gastric juice, gall, bile, urine, milk, 

 tears, &c. When any nerve connected with a gland is irritated the gland 

 becomes active in its function of secretion. " If, for example, the 

 nerves which pass into the salivary gland are irritated, the saliva may be 

 made to ooze in a stream from the mouth of the gland. " The simple 

 glands, like the muscles, possess regular electric activity. Where a 

 large number of the simple, bottle-shaped skin glands ' 'occur regularly, 

 arranged side by side, it is found that the lower surface, that which 

 forms the base of the glands, is positively electric, while the upper sur- 

 face, that which forms the exit duct of the gland, is negatively electric. " 

 ( Rosenthal. ) When glands are irritated and made active the ' ' negative 

 variation, "or decrease of gland current, takes place the same as in the 

 muscle. That is, electrical tension disappears in work. The mucous 

 membrane of the stomach and intestinal canal also furnishes electrical 

 action, according to experiments on the alimentary canal of the frog. 

 The direction of nervous energy to any of the glands, stimulates their 

 normal activity. This can often be accomplished by simply directing 

 attention to the organ, or to some act in which its functions are con- 

 cerned, for, as will appear further on, mental action may become cur- 

 rent electricity. Even mere states of feeling may produce effects on 

 certain glands when there is neither attention nor consciousness of them 

 or their functions. The secretion of milk in the mammary glands of a 



