The action of respiratory stimulants in morphine and heroin poisoning.

In the experiments on cats previously reported, it was apparent that the action of morphine and heroin on respiration was limited to a depression of expiration, and that an extremely slow rate and respiratory failure depended on a primary depression of the circulation. These observations have been confirmed in every case in experiments on dogs, and in most experiments on rabbits, though in one experiment heroin caused temporary respiratory failure and asphyxial effects on the blood pressure of a rabbit, and circulatory depression was usually less marked in rabbits after morphine or heroin than in dogs or cats. The extremely slow regular breathing of advanced morphine or heroin poisoning never occurred, in dogs or rabbits, unless circulation was definitely depressed, and the appearance was that of vasomotor failure.

As respiratory stimulants, atropine, caffeine, and camphor were tried; digitalis was used as a circulatory stimulant; and inhalations of CO₂, of 7 to 10 per cent strength, were also used, when respiration was seriously depressed by morphine or heroin.

Atropine stimulated respiration only exceptionally, and the stimulation appeared as an increase in depth but never in rate. As a rule, it either had no effect, or it added to the respiratory and circulatory depression especially if large doses were given—2 to 10 mg. to a dog.

Caffeine was the most reliable and safest stimulant, often increasing both rate and depth, and sometimes bringing back active expiration, especially if it improved the circulation. Large doses did no harm unless they depressed the circulation, when respiratory failure usually followed.

Camphor produced striking stimulation of respiration and circulation in one experiment on a rabbit, in 20 mg. dose, but in all other attempts on rabbits and dogs it either had no effect, or produced circulatory depression and respiratory failure