Alcohol has long been held in repute as a respiratory stimulant. Many observers have noted a small increase in the activity of the lungs following upon the administration of a moderate dose of alcohol, even when care has been taken to keep the subject in repose after the dose. Not all the experimenters, however, agree in this conclusion. Thus Loewy1 gave, separately, doses of 35 c.c. and 60 c.c. of alcohol to each of two subjects, one habituated to alcohol, the other not; but only in the case of the latter subject, taking the larger dose, was any increased respiratory activity detected.

More modern researches point in the same direction. They indicate that in normal conditions there is probably no stimulant effect of any practical importance produced on the respiration by a moderate quantity of alcohol.

An outline of a recent research carried out by Higgins2 may be given. The nervous centre governing the respiration acts normally in response to the stimulating action of the carbon dioxide in the blood, increasing or decreasing the respiratory activity in such manner as to keep the proportion of carbon dioxide practically constant. If alcohol affects the respiratory nervous centre, increasing its excitability to the normal proportion of carbon dioxide and therefore augmenting the respiration, the proportion of this gas in the blood will fall. But the gases of the blood are in equilibrium with those of the alveolar air of the lungs, and this air can be analysed. If the analysis shows that the proportion of carbon dioxide diminishes after alcohol has been taken, the inference (leaving other factors out of account for the present purpose) is that the alcohol has stimulated the nervous centre and increased the respiratory activity.

Higgins experimented on seven subjects, including both abstainers from and regular users of alcohol. Doses of 30 c.c. and of 45 c.c. were given, suitably diluted with a flavouring mixture, and each experiment was controlled by another in which the subject took the same flavouring mixture without the alcohol. The patients were kept carefully at rest, to guard against production of carbon dioxide through muscular activity. It was found that in some of the experiments there was, in fact, a small reduction of carbon dioxide in the alveolar air after the alcohol had been taken, indicating a slight increase in the excitability of the respiratory centre. This effect, however, was counterbalanced by a diminished production of carbon dioxide by the body, so that the net result on the breathing was almost nil. The volume of air breathed per minute was either unchanged or slightly diminished.

1 Pfluger's Archiv, 1890, 47, 601.

2 J. Pharm. Expt. Ther., 1917, 9, 441.

Practically, therefore, the effect of a moderate dose of alcohol on the respiration would appear to be trivial. "The only important effect of alcohol on respiration is the paralysis of the respiratory centre by large doses, which is the cause of death in (alcoholic) poisoning."1