Granting, then, the possibility of taking into the blood more than the normal amount of the gas, it yet remains true that in many healthy persons no marked effect is to be noted from inhalations of fifteen to thirty litres of oxygen, unless it be a sense of warmth in the mouth and at the epigastrium (Husemann).

Naoumoff and Beliaieff, breathing it for seven to seventeen minutes, found no appreciable change in pulse or temperature, whilst in dogs made to breathe alternately air and oxygen, the temperature rose sometimes with the latter a few tenths of a degree, and there seemed some dilatation of capillaries (Abstract, Lancet, i., 1875).

Mr. Savory, partly following Regnault and Reiset, and partly relying upon observations with animals which showed no increase of temperature under oxygen-inhalations, has also argued that these can exert no effect on the system; but Dr. Edward Smith has pointed out that such experiments, to be conclusive, should extend over long periods, and take account of changes in diet, etc.; he himself found evidence of increased chemical change under oxygen.

In some persons, inhalation of the gas causes temporary nerve-symptoms, such as exhilaration, sense of vigor, heat of skin, tingling of fingers, and even pain referred to the fifth nerve (Husemann). I have myself observed all these symptoms, except the last, immediately after the inhalation; also some giddiness, and some rise of pulse, probably from extra effort in breathing; in the delicate, improved appetite, improved motor power, and sleep have followed. I can corroborate this observation, which has been made by Birch, Demarquay, and others. Oxygen, then, is not without effects, though these vary with different individuals, and we cannot yet reduce them to precise scientific expression.

Dr. Richardson, judging partly from a case in which the blood passed from the lungs back to the right heart, and so circulated "surcharged with oxygen," states that such excess leads to great exhaustion of muscular and nerve-power and constant perspiration (Lancet, ii., 1878), but the conditions are not simple enough for asserting that these symptoms are solely due to the gas. If an animal be kept in a closed vessel full of oxygen, it dies - we cannot exactly say why. Broughton discovered that rabbits, guinea-pigs, sparrows, etc., thus kept, were at first lively and excited with quickened circulation and respiration, but passed in an hour's time into a weakly, depressed condition, and finally died, although the air in the bell-jar was still pure enough to rekindle a flame. Dr. Richardson obtained similar results with oxygen that had been breathed and then purified, and he inferred that some principle essential to life was removed from the gas in the process of respiration (British Medical Journal, ii., I860). He found in the animals after death a condition of "hyperinosis," and Demarquay, who met with analogous results, describes the volume of the blood as apparently much increased, the muscular and other tissues brightly red, the venous blood distinctly to be recognized, but less dark than usual, and more quickly reddened on exposure, the lungs congested being "intensely red," and all the viscera unduly vascular. The same observer states that a small amount of gas may be passed directly into the blood by careful intravenous injection, and in such cases, after death, the spleen is markedly redder than usual.

Theory Of Action

Rosenthal concluded from certain experiments that an increased amount of oxygen in the blood caused "apnoea," for if, after blowing in air for twenty to sixty minutes through the trachea of an animal, the artificial respiration be suddenly interrupted, the animal remains motionless and without breathing for twenty to forty seconds, then respiratory action, at first weak, ultimately normal, returns. Now, this being an opposite condition to one of dyspnoea, and the latter being dependent upon want of oxygen and consequent extra stimulus of the respiratory centre, he argued that apnoea must depend on overmuch oxygen. Ewald also, by experiment, determined some slight increase of oxygen in the blood in apnoea; Hering not so. In any case there is really no causal relation between the two facts (Buchheim: loc. cit.), nor is apnoea complained of after oxygen-inhalation or condensed air treatment.

Experiments of this nature, though very interesting, cannot be taken as practical guides in the clinical use of the gas, and, under ordinary conditions of inhalation, oxygen never causes the lung-inflammation and exaggerated vital processes predicted by Beddoes and others.