o04 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



The action of drugs on the heart can be studied still better in 

 the frog than in mammals, as the heart of the former can be 

 completely separated from the body, so that the drug can be 

 applied to it alone. After its removal it continues to pulsate 

 just as before, and, consequently, any action of the drug on the 

 rhythm or force of its beats can be very easily noticed. The 

 usual way of making experiments on this subject formerly was 

 to take out the heart and lay it in a solution of the poison, or, 

 what was better, to take two glasses containing solution of chlo- 

 ride of sodium (half per cent.) and add a little of the drug to one 

 of them. A frog's heart was then laid in each, and the beats of 

 the poisoned compared with those of the unpoisoned one. Both 

 of these plans are inferior to that of Ludwig, who supplies the 

 heart with serum so as to keep it as nearly as possible in a nor- 

 mal condition, and attaches to it a manometer, so that it may 

 itself register the number and form of its beats, and give more 

 exact indications than could be obtained by merely looking at 

 it. The apparatus which he and Cyon first used, and which is 

 figured in his Arheiten for 1866, has been considerably modified 

 by Dr. H. P. Bowditch, and is shown in Fig. 136. It consists of 

 a bent glass tube (c c' c''), which is supported by a glass plate 

 (d). The frog's heart (a) is connected to the ends of this tube 

 by means of india-rubber tubing and two glass cannula?, one of 

 which (b) is tied into the vena cava and the other (b^) into the 

 aortic bulb. The tube has three openings, each of which is 

 furnished with a three-way glass stopcock. By means of one of 

 these (o) it can be filled with serum from a reservoir (k or k'), 

 and the stopcock may be so turned as to allow serum to enter 

 the part of the tube above it, the part below it, or both together, 

 or the communication with K may be shut ofif while the lumen 

 of the tube remains open. By c', the serum which has been 

 already used is allowed to escape, when a fresh supply is giyen, 

 and g" allows the tube to communicate with a manometer (m), 

 on the mercury in which a fine pen floats and registers its oscil- 

 lations on a revolving cylinder (q). Each time the heart con- 

 tracts it drives the serum with which it is filled out of the 

 ventricle, round the tube, and back through the vena cava into 

 the auricle, and at the same time raises the mercurial column in M. 



