Thus far, we have been considering muscular responses, but now we must turn our attention to the glands. The glands are often affected during emotion, as witness the shedding of tears in grief, sweating in anger, the dry mouth during fear due to inhibition of the salivary glands, and the stoppage of the gastric juice during anger, as just noted. These particular glands all pour out their secretions either upon the skin or upon the mucous membrane of the mouth, stomach, etc.; and such secretion is called "external" in distinction from the "internal secretion" of certain other glands which may be called the glands of internal secretion or the "endocrine glands". Internal secretions are {123} discharged into the blood vessels, and carried by the blood to all parts of the body, and they have important effects on the activity of various organs.

Of the endocrine glands, we will mention only two, which are known to play an important part in mental life.

The thyroid gland, situated in the lower part of the neck, is necessary for normal brain activity. Without its internal secretion, brain activity is very sluggish.

The adrenals, two little glands located near the kidneys (whence their name, though they have nothing to do with the kidney in function), have a close connection with such emotions as anger. In the normal or neutral state of the organism, the adrenal secretion oozes slowly into the blood, and has a tonic influence on the heart and muscles. But let an anger stimulus occur, and within a few seconds the adrenals are secreting rapidly; all the organs soon get a big dose of the adrenal secretion, and some of them are strongly affected by it. It hastens and strengthens the action of the heart, it causes the large veins inside the trunk to squeeze the blood lagging there back to the heart; and by these two means greatly quickens the circulation. It also affects the liver, causing it to discharge large quantities of stored sugar into the blood. Thus the muscles of the limbs get an unusual quantity of their favorite fuel supplied them, and also, by the increased circulation, an unusual quantity of oxygen; and they are enabled to work with unusual energy. The adrenal secretion also protects them in some way against fatigue.

While the adrenal secretion is thus exerting a very stimulating influence on the limb muscles, it is having just the opposite effect on the digestive organs; in fact it is having the effects described above as occurring there during anger. These inhibitory effects are started by the stomach nerves, but are continued by the action of the adrenal juice {124} on the stomach walls. The rapid secretion of the adrenal glands during anger is itself aroused by the nerve running to this gland.