330 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



But external respiration may be arrested or diminished, the 

 blood rendered venous, the respiratory movements consequently 

 increased, and dyspnoea and asphyxia produced by preventing 

 the blood from reaching the air, as well as by preventing the 

 air from reaching the blood. The blood may be prevented from 

 coming into relation with the air: (a) By stoppage of the 

 heart ; (b) By embolism of the pulmonary artery ; (c) By con- 

 traction of the capillaries of the lung. 



(a) By Stoppage of the Heart. — When respiration is suddenly 

 impeded in any of these ways, the breathing becomes panting ; 

 and when it is suddenly stopped altogether, asphyxial convul- 

 sions occur. When the jugular vein is chosen for the introduc- 

 tion of drugs into the circulation, they come very quickly and 

 without much previous dilution with blood nto contact with 

 the heart and pulmonary vessels, and thus affect them more 

 strongly than they would do if injected subcutaneously, or into 

 one of the veins of the extremities. When a large dose of 

 quinine is thus injected, the heart may be stopped at once, and 

 convulsions ensue. Any alteration of the heart's action pro- 

 duced by a drug is easily noted by means of a needle fixed in 

 the ventricle. 



(h) By Embolism of the Pulmonary Artery. — This cause of 

 interrupted respiration may easily lead an inexperienced 

 observer to very erroneous conclusions regarding the action of 

 a drug. Supposing him to inject an unfiltered solution of some 

 extract into the jugular vein, he may find the respiration 

 almost immediately afterwards become panting ; the eyes start 

 from their orbits, the limbs become convulsed, the head drawn 

 back, and after one or two quivering contractions, life becomes 

 extinct. He at once concludes that the substance he has 

 injected is one of extreme activity, whereas it may be really 

 quite inert ; the violent symptoms which followed its injection 

 being due to the extract being imperfectly dissolved, and the 

 suspended particles producing embola in the pulmonary vessels. 



In some experiments which I made on condurango, I was at 

 first misled by this circumstance, and believed that the drug 

 had a tetanising action, like that of strychnia, as convulsions 

 came on immediately after injecting a solution of the extract 



