832 EXPEUIMEXTAL INVESTIGATION OF THE ACTION OF :\1EDICINES. 



much, it ought to be laid hold of and ligatured. Artificial 

 respiration being carefully and regularly kept up by means of 

 a metronome, the colour of the lungs, tlie size of each ventricle, 

 and the number of cardiac pulsations is observed, the drug 

 injected, and the observation repeated. The pulsations nmst 

 be counted, because slowness of the heart's action, by affording 

 time for the accumulation of venous blood in the right ventricle, 

 would cause it to become distended, although there were no 

 obstruction to the pulmonary circulation. When the drug to 

 be experimented on is not a solution but a vapour, it must be 

 passed into the lungs by the method already described {British 

 Medical Journal, May 20, 1871). 



In this way, I have ibund that muscarin causes contraction 

 of the pulmonary vessels, and produces dyspnoea (see British 

 Medical Jonrncd, November 14, 1874), although the heart con- 

 tinues to beat, and artificial respiration is vigorously kept up. 

 The lungs become pale, the right side of the heart sw^ells tip, 

 and the left side and arteries become empty, as represented 

 diagrammatically in Fig. 145. The vapour of chloroform blown 



Tia. 11 1. 



riG. 145. 



!FiG. 144. — Diagrnm representing the normal condition of tlie circnlation. 

 Eoth the reins and arteries are n^oderately full ; tlie two sides of the heart are 

 of much the same size, and the circulation through the lungs is free. 



Fig. 145. — Diagram representing the condition of the circulation after the 

 administration of muscarine. The veins are distended, tlie arteries empty ; the 

 right side of the heart is much enlarged, the left side collapsed, and the 

 circulation through the lungs almost entirely arrested. 



into the lungs causes a similar appearance, but it arrests the 

 cardiac pulsations more or less completely at the same time. 



