Theory Of Action

It is easier to ascertain, than it is at present to explain these facts. Hoppe-Seyler suggests that the red corpuscles lose for a time their power of giving up oxygen in the capillaries - that oxidation of tissue is suspended (Untersuchungen, 1866, erst. Heft, s. 140). Geinitz argued that a change in the physical form of the corpuscles would explain change of color, and found that the acid mixed with blood outside the body caused various alterations of their form (Pfluger's Archiv, Bd. iii., 1870): but according to Preyer the blood of a poisoned animal taken from the vessels directly after death, and examined by the microscope, exhibits no change in the character of the corpuscles (Chemismus, Leip-sic, 1840). He inquires whether the deepened breathing could for a time induce a hyper-oxygenated condition, as in animals dying from apnoea and found by Pfluger to have light-red blood (Archiv, i., p. 106), or whether the increased blood-pressure could drive the blood so quickly through the capillaries as to prevent its giving up oxygen as usual.

I cannot satisfy myself as to a clear explanation, but believe that during the first stage of cyanic poisoning oxidation is arrested, and that the venous condition of blood found in later stages of poisoning is connected with spasm of the pulmonary arterioles, and paralysis of the respiratory and cardiac muscles.

It would seem that no permanent toxic combination is found with the corpuscles; they are not at once fatally spoiled, nor is oxygen wholly driven out, but for the moment (and it may be finally) its interchange with tissues is prevented. The results of many careful spectroscopic examinations by Preyer and others, and of many laborious gas analyses by Gaethgens, confirm this view: the red blood shows still the absorption bands of oxyhaemoglobin, and the dark blood those of haemoglobin, with little or no combined oxygen: outside the body, indeed, prussic acid destroys haemoglobin (forming a new compound, cyanohaemoglobin, which is destitute of ozonizing power), but apparently does not do so during life. Laschkewitsch could not detect such compound, but on the contrary found oxyhaemoglobin (Reichert's Archiv, 1868), and more recently, Hiller and Wagner, examining blood while still within the mesenteric vessels, obtained characteristic though feeble lines of oxyhaemoglobin (Lancet, ii., 1877). If withdrawn from the body, the dark blood, shaken up with oxygen, resumes its normal red tint, and a most important practical point - the condition just described may be remedied during life by securing access of additional oxygen by artificial respiration.

Gaethgens proved (1) that the property of de-oxygenated blood to abstract oxygen from surrounding media is not destroyed by prussic acid; (2) that blood saturated with oxygen exposed to the action of prussic acid gives off no oxygen, and that substances which would usually withdraw oxygen from fresh blood do so with much difficulty under the influence of the acid. Both oxygen and carbonic acid are excreted in less than normal total quantity during the poisoning (on account of the slow rate of the breathing), but not only is the actual percentage of carbonic acid in the expired air less than normal, but the percentage of oxygen in the same expired air is greater than normal - i.e., it has not been used up in the system.

Synergists

Cyanides owe their activity to prussic acid, and exert a similar action. Cherry-laurel water, and essence of bitter almonds, owe their chief properties to the same acid. All substances which hinder haematosis, or the union of oxygen with the blood-corpuscles - such as arsenic, antimony, and most sedatives - favor the action of hydrocyanic acid.

Antagonists - Incompatibles

The effect of medicinal doses is lessened by diffusible stimulants, by strong acids or alkalies, and by opium (Gubler). Warmth quickly volatilizes the acid, otherwise it favors its action. The most dependable antidote to poisonous doses is oxygen, which is best introduced into the system by artificial respiration.

Preyer strongly recommends atropia as a "dynamic antidote," since it acts upon the vagus nerve in a manner contrary to that of hydrocyanic acid (v. Vegetable Kingdom). I must agree with Boehm and others that his observations are somewhat wanting in scientific accuracy, as when he speaks of injecting "a little atropia," or says simply, "Injected sulphate of atropia, and afterward a rather large dose of prussic acid, which would assuredly have caused death" ("Versuche," p. 74, 36-37), and although Bartholow, Lecorche, and others have failed to obtain confirmative evidence, still they hold true to a certain extent. A practical difficulty in their useful application must always be the extremely rapid course of cyanic poisoning, and the (comparatively) slow diffusion of atropia; to be of any service, the alkaloid would have to be used almost on the instant of poisoning.

Sal-ammoniac was strongly recommended by J. Murray (Edinburgh Philosophical Journal, 1822), and although Orfila and Elwert showed that it could not be depended upon as an antidote, I think this and other compounds of ammonia well deserve further trial. Modern observation credits the drug with a power of directly stimulating the respiratory centres (v. p. 255), and this, in addition to its general stimulating power, seems specially to indicate its use in cyanic poisoning.

Chlorine and chlorine water have been used with advantage by A. Chevallier and Orfila, but they are not manageable. Turpentine, though recommended as a specific antidote, has only value as a stimulant. I cannot see that phosphorus offers a resource of value, nor can much be expected from coffee.

Some indefinite evidence exists as to an antidotal power possessed by strychnia. Thus, a puppy that had taken 1/2 gr. of prussic acid quickly recovered after swallowing a dose of the alkaloid (Medical Times, ii., 1859), and some other instances are reported (Lancet, i., 1868). Stannius also found that strychnia-convulsions were modified by the acid, but Dr. Lauder Brunton concluded "that although the acid may somewhat lessen the convulsion, it cannot be employed as an antidote to strychnia with any hope of success," and G. Harley thought "that it rather hastened death from strychnia" (Medical Times, ii., 1861).

Silver and metallic oxides generally, form insoluble compounds with prussic acid, and fresh proto-carbonate of iron has been recommended as antidotal by Messrs. Smith ("Medico-Chirurgical Transactions," ii., 1865); practically, however, their influence can scarcely be exerted quickly enough.

It remains that artificial respiration is the main resource in all forms and stages of cyanic poisoning - it may be carried out in the ordinary methods, or excited by the sudden affusion of water, first cold and then hot, thrown over head and chest. This does not exclude the use of an emetic, the application of ammonia to the nostrils, or even its injection into the veins, while stimulating frictions and warmth should be applied to the limbs; by the steady use of these means, patients have revived from apparently hopeless insensibility, and if life can be prolonged for an hour, the chances of recovery become greatly increased.

Therapeutical Action (External)