Characters. - A yellowish liquid with a strong ethereal, fruity smell. When freely exposed to air it decomposes, leaving a large residue of amyl alcohol.

Solubility. - Insoluble in water, but soluble in all proportions in alcohol, ether, and chloroform.

Preparation. - By distilling dilute amyl alcohol with nitric acid, sulphuric acid and copper wire. The distillate is washed with caustic soda to remove hydrocyanic and other acids; the moisture removed by potassium carbonate, and the nitrite purified by fractional distillation between 262° and 270° F. (128° - 132° C).

Impurities. - It is apt to contain free acid, nitrate of amyl, nitro-pentane.

Tests. - The physiological test is the most certain. One or two sniffs from a bottle containing the nitrite are usually sufficient to produce flushing of the face and fulness in the head. If the preparation is impure or has lost its strength, this effect does not occur. Some specimens are entirely inert.

Physiological Action. - When mixed with blood it forms methaemoglobin, which is not so readily de-oxidised as haemoglobin itself. The blood, under the influence of the nitrite, becomes of a dark chocolate colour, both in the arteries and veins, and oxidation in the body is interfered with; so much so that in rabbits convulsions almost exactly resembling those of ordinary asphyxia are very rapidly produced by the inhalation of the drug. The methaemoglobin may be broken up by reducing agents, and the blood will then take up oxygen again. It is therefore probable that, when the venosity of the blood becomes great, the unoxidised products of tissue-waste will act as reducing agents, and again restore the internal respiration. When inhaled, nitrite of amyl causes at first a short dry tickling cough, followed in about half a minute by flushing of the face, throbbing of the carotids and their branches, a quicker and fuller pulse, a feeling of tension in the head, sometimes lacrimation, quickened respiration, and giddiness. The giddiness is more especially felt if the patient is sitting up. If the dose of nitrite be large the respiration becomes very quick, laboured, and dyspnoeic. The blood-pressure is very greatly lessened by nitrite of amyl, the diminution being chiefly due to dilatation of the arterioles. The pulse in man and in dogs is very much quickened by it. In rabbits the acceleration is not so great. This appears to show that the quickening is in a great measure due to diminution in the tone of the vagus-roots in the medulla caused by the fall of blood-pressure. The dilatation of the arterioles appears to be due to weakening or paralysis, either of the muscular walls of the arterioles themselves, or of the vaso-motor ganglia in or near them. This is shown by the fact that the nitrite of amyl lowers the blood-pressure in animals, even after the cord has been divided just below the medulla. It has been objected to this that Bernheim has found that when the capillaries are dilated by nitrite of amyl they may still be made to contract by irritation of the vaso-motor nerves; and he concludes from this that the dilatation is due rather to paralysis of vaso-motor centres than to vaso-motor nerves, or to the arterioles. It is possible that the dilatation may be partly due to weakening of the vaso-motor centres also; but Bernheim's objection is altogether without force, because in animals killed by curare, the muscles will still contract on the application of an electric current to the motor nerves. In this case the nerves are so far paralysed that they will no longer respond to the stimuli sent down from the nerve-centres, although they will do so to strong currents, and probably the same thing occurs with the muscular walls of the arterioles when paralysed by nitrite of amyl.

Action on Muscles. - The voluntary muscles are not paralysed in animals poisoned by nitrite of amyl, but when the muscles of a frog are exposed to the vapour they soon lose their contractility. It was stated by Dr. Richardson that nitrite of amyl, like curare, paralysed the ends of the motor nerves, and that it acted in consequence as an antidote to strychnine. On repeating his experiments other observers have failed to detect any paralysis of motor nerves. I have found that nitrite of amyl alone does not paralyse them, nor does strychnine alone; but if a frog be poisoned with strychnine after one leg has been protected by a ligature from the influence of the poison, and is then exposed to the vapour of nitrite of amyl, the joint action of the strychnine and nitrite paralyses the ends of the motor nerves, while the nerves of the limb protected from the strychnine retain their irritability, although both were equally exposed to the nitrite of amyl.1

Action on the Nervous System. - It lessens reflex action, apparently by its action on the spinal cord.

On the Urine. - When nitrite of amyl is given to animals either by inhalation or hypodermically, sugar appears in the urine.

Uses. - The action of nitrite of amyl in causing flushing was first observed by Guthrie, and Dr. B. W. Richardson recommended it as a remedy in spasmodic conditions, from the power he thought it to possess of paralysing motor nerves. In the spring of 1867 I had opportunities of constantly observing a patient who suffered from angina pectoris, and of obtaining from him numerous sphygmographic tracings, both during the attack and during the interval. These showed that during the attack the pulse became quick, the blood-pressure rose, and the arterioles contracted; for the form of the pulse-curve was such as could only be caused by contraction of the arterioles (Fig. 173). The pain, which came on every night, lasted for one and a half or two hours. All other remedies were nearly useless, though bleeding always removed the pain for one night. It seemed probable that the great rise in tension was the cause of the pain, and it occurred to me that if it was possible to diminish the tension by drugs, instead of by bleeding, the pain would be removed.