110 EXPERIMENTAL PHARMACOLOGY 



the margins of the chest avails as shown in Fig. 106. Tie 

 these ends, draw the chest wall open, and fasten the strings 

 to the operating board as shown in Fig. 107. 



This fully exposes the lungs and the heart which is cov- 

 ered by the pericardial sac. Did you see the anterior 

 mediastinum? What became of it? With scissors open 

 the pericardium in the midline. Then bring the cut edges 

 of the pericardium out laterally and sew them (with two 

 or three stitches on each side) to the chest wall. This 

 forms a kind of hammock in which the heart lies. The 

 animal must be given sufficient ether to keep it quiet all 

 the time. Observe carefully the beating of the heart and 

 the movements of the lungs. Did the blood-pressure fall 

 much when you opened the chest? It should not. Does 

 the heart rise and fall as the lungs are inflated and de- 

 flated? If so, try to reduce the extent of inflation a little 

 and see if the animal does Avell (blood-pressure remains 

 normal and convulsive movements do not appear). This 

 rise and fall of the heart is the most troublesome thing 

 concerned in the taking of heart tracings. Now take the 

 cardiometer (Fig. 108) and stretch the rubber membrane 

 outward from the opening, rolling part of the edge of the 

 membrane back over the metal rim. Now place the cardi- 

 ometer down over the heart (ventricles only, see Fig. 107) 

 and bring the membrane down to the auriculo-ventricular 

 groove. Roll the edge of the membrane off the metal part 

 and allow the opening in the membrane to close around the 

 auriculo-ventricular groove. Does the blood-pressure re- 

 main normal? If not, wait a little and if necessary re- 

 adjust the cardiometer. Connect the cardiometer tube with 

 a recording tambour which may write either above or be- 

 low the blood-pressure, depending on whether the pressure 

 is low or high respectively. Adjust all writing points and 

 take two or three inches of "normal" tracing. The cardi- 

 ometer record should be one or two inches in amplitude. 



