In the first place, the medulla contains numerous nerve cells, belonging to the vegetative, also called the sympathetic nervous system. But these nerve cells are merely minor notes of the symphony. The motif is settled by a majority of large, granular cells, which stain a distinctive yellowish-brown when the gland is fixed in a solution of bichromate of potash. All chromium salts, in fact, stain the therefore labelled chromaffin cells. The characteristic staining power appears to be dependent upon, or correlated with, the presence of the internal secretion of the medulla of the adrenal, adrenalin. For the content of adrenalin, as calculated chemically, and the depth of stain as seen under the microscope, rise and fall together. Chromaffin reaction and adrenalin content go together. The poisonous skin glands of the toad have been found to give a marked chromaffin reaction, and to contain a large amount of adrenalin. Other masses of cells in the human body, especially along the course of the sympathetic nervous system, have been shown to give the reaction and to contain adrenalin. The erratic Brown-Séquard pounded and hammered away for more than thirty years on the importance to life of the adrenal glands, since death occurred so quickly after their removal. But it was not until Schaefer, the Scotch physiologist, (who has done more than any other living man to stimulate study of the internal secretions) found that an extract of them, when injected into a vein, produced a remarkable though temporary rise of the blood pressure, that a real enthusiasm for its investigation was generated. As the upshot, a number of other significant properties besides the first of blood-pressure raising, have been put down to its credit. Chemical tests demonstrated that it originated in the medulla. The exact amount of it present in the medulla, in the blood issuing from the adrenals and in the circulation in general have been determined. The concentration in the blood is about one part in twenty million, while there is about a hundred thousand times as much stored in the gland as reserve. In infections and intoxications, after muscular exertion, and with profound emotions, there is a decrease of it in the gland and an increase in the blood. Pain and excitement, especially fear and rage, will bring about its discharge from the gland. With its entry into the blood, there is a tremendous heightening of the tone, a _tensing_, of the nervous system. The nerve cells become more sensitive to stimuli, more sugar is poured into the blood from the liver, more red blood corpuscles are squeezed into the circulation from the blood lakes of the liver and spleen. There is a redistribution of the whole blood mass, a good deal of it being withdrawn from the internal viscera, and hurried to the skeleton muscles and the brain. The heart beats more strongly, the eye sees more clearly, the ear hears more distinctly, and the breathing is more rapid. The temperature rises, the hair of