Suppose we have a tame cat, that knows us well, and, after feeding her a good meal containing some substance that is opaque to the X-rays, suppose we place her on a table and pass X-rays through her body, so as to get a visible shadow of the stomach upon the plate of the X-ray machine. Well and good; the cat is contentedly digesting her meal, and the X-ray picture shows her stomach to be making rhythmical churning movements. In comes a fox {122} terrier and barks fiercely at the cat, who shows the usual feline signs of anger; but she is held in position and her stomach kept under observation--when, to our surprise, the stomach movements abruptly cease, not to begin again till the dog has been gone for perhaps fifteen minutes. The churning movements of the intestine cease along with those of the stomach, and, as other experiments show, even the gastric juice stops flowing into the stomach. The whole business of digestion halts during the state of anger. So anger is an organic state, without doubt. At least in cats--but the same is found to be true of man, and hence the excellent rule not to get angry on a full stomach. Stomach-inhibition is not the only internal response during anger. The heart, so long regarded as the seat of the emotions, does beat more forcibly than usual; and the diaphragm, where the old Greeks located the emotions, does make extra-strong breathing movements. There are yet other and more curious changes that have recently been discovered by the physiologists. Glandular Responses During Emotion 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.