Medulla

The respiratory center is somewhat stimulated. The vagus center is depressed.

Eye

Besides the temporary blurring of the sight, which is due, perhaps, to dilatation of the retinal arteries, dark objects may appear to be surrounded by yellow and blue rings.

Muscle

Other muscles are not so much depressed as those of the arteries, yet in bronchial asthma the bronchial muscles may be enough depressed to lessen their spasmodic contraction and bring relief. This is commonly brought about by the inhalation of the fumes from burning potassium nitrate. Occasionally spasm of the ureter or common bile-duct from the presence of a stone has been overcome by nitroglycerin.

Temperature may be lowered, owing to dilatation of the cutaneous vessels and the accompanying sweating, but this is not a marked effect.

Excretion is by the kidneys, chiefly as nitrates. After large amounts of nitroglycerin this may appear unchanged. The dose is too small to have any appreciable effect upon the amount of the nitrogen elements of the urine.

Kidneys

With the nitrites, any change in the amount of urinary excretion depends upon the relation between the fall in general blood-pressure and the dilatation of the renal arteries. The effect is not constant, though in some cases marked diuresis will follow nitrite administration.

Toxicology

It is a common thing for therapeutic doses of amyl nitrite or nitroglycerin to be followed immediately by a pounding heart, flushing of the face and neck, and throbbing and fulness in the head, with a feeling "as if the top of the head were coming off." In addition, there may be confusion of ideas, blurring of the sight, dizziness, and a feeling of faintness. Such effects are distressing to the patient, but are quickly recovered from. Except for the flushing of the face, they are not nearly so striking when the patient is lying down, and would seem to be due to low cerebral blood-pressure. Occasionally large doses produce cyanosis and collapse. A student in our laboratory fainted after the inhalation of 5 minims of amyl nitrite. He was in the upright position when the drug was administered, and his systolic pressure had been recorded as only 88 mm. On the other hand, D. D. Stewart gave a man 50 minims of a 10 per cent. solution of nitroglycerin four times a day - i. e., 20 grains of nitroglycerin in a day - without untoward effects. Very large doses have been given to animals without causing death and there are no reported cases of death in man. Any nitrite may be followed by a headache, but persistent severe headache is most common with nitroglycerin or erythrol tetranitrate

Therapeutics

1. To lower abnormally high general arterial pressure, as in chronic nephritis, the dose being administered from three times a day to every hour. It is especially prone to fail in cases with edema. But it must be noted that in cases with long-continued high arterial pressure it is not considered wise to bring the arterial pressure down to normal, for the high pressure may really be a response to a need of one or other organ for a greater supply of blood. In nephritis, for example, the lowering of a chronically high pressure may result in suppression of urine. On account of the ephemeral action of the drug, comparative daily blood-pressure tests should follow the doses at a fixed interval of time.

2. To lessen peripheral resistance in some cases of weak heart, as in aortic insufficiency.

3. To dilate the peripheral arteries in local vasomotor spasm, as in Raynaud's disease and erythromelalgia.

4. To relax the coronary arteries in angina pectoris. The drug may be indicated even if the general blood-pressure is not high; but it is said to be contraindicated in marked coronary sclerosis with myocarditis.

5. To relax the bronchial muscles in asthma, especially by burning niter.

6. As a diuretic and diaphoretic in colds and mild fevers - the spirit of nitrous ether, the alcohol of the spirit being probably of as much value as the ethyl nitrite.

7. Amyl nitrite has also been employed to overcome chloroform collapse. This is on the theory that it lessens peripheral resistance and spares the exceedingly weak heart. The author has restored mice by amyl nitrite when they were apparently almost dead from chloroform. According to Muhlberg and Kramer, it is effective in preventing the stoppage of the heart in the first or second stages of ether or chloroform anesthetization. Yet some experiments with chloroform containing 2 per cent. of amyl nitrite have shown this mixture to be more toxic than chloroform alone, so the subject needs investigation.

Administration

For immediate and intense effect, amyl nitrite by inhalation. For general arterial dilatation, nitroglycerin, which acts almost as promptly by mouth as when given hypodermatically, or sodium nitrite or erythrol tetranitrate. For bronchial relaxation, inhalation of amyl nitrite, or the fumes of burning potassium nitrate, or nitroglycerin by mouth or hypodermatically. "Asthma powders" usually contain potassium nitrate with stramonium, lobelia, tobacco, or cubebs.

There are two other arterial dilators in common use, viz., potassium iodide and chloral hydrate. They do not show any dilator effect in normal animals, but at times seem to have decided effects when there is an abnormally high blood-pressure. So far experiments with animals have not taught us their exact modus operandi. We speak of these drugs again.

Measures For Decreasing The Volume Of The Blood

Blood-letting, venesection, or phlebotomy is the process of removing blood from a vein, usually the median cephalic or median basilic. To increase the venous flow when necessary, a light tourniquet may be placed about the upper arm, and the forearm gently massaged upward, or the patient made to open and close the hand. A hollow vein needle is inserted into the vein and 4 to 20 ounces (120 to 600 c.c.) allowed to flow. In lieu of a needle the vein may be cut down upon, tied off, and snipped with scissors.