The height of the curve traced by the pen depends very much 

 on the amount of serum which the heart contains, being 

 very much higher when the heart is full: and it must, there- 

 fore, be equally filled each time, or very different tracings will 

 be obtained. For this purpose I use, as reservoirs for the serum, 

 fountain-bottles, in the mouth of which it always stands at the 

 same level, and, consequently, always fills the heart at the same 

 pressure. One of them (k) is filled with pure serum, and the 

 other (k') with serum to which a certain amount of the drug to 

 be tested has been added. 



For the purpose of introducing the cannula into the heart, 

 the brain and cord of the frog are destroyed by a piece of wire, 

 and the animal fixed on its back to a board. A Y-shaped in- 

 cision, with its apex at the lower end of the sternum, and its 

 Jimbs extending upwards and outwards towards the forearms, is 

 then made in the skin, and the flap turned back or cut off. The 

 sternum is then removed in a similar way. The pericardium is 

 next opened, the cut being made while the heart is contracted, 

 so as to avoid injuring it. The apex of the heart itself is then 

 turned upwards, and two ligatures are passed underneath a 

 small vein which runs from its posterior surface to the pericar- 

 dium. The ligatures are tied, and the vein is cut between them. 

 The pericardium must now be removed entirely from the heart, 

 and the vena cava superior and the right branch of the aorta 

 tied. The vena cava inferior is carefully isolated ; a ligature is 

 passed under it, a short and wide cannula tied into it, and 

 another into the left branch of the aorta. The heart is then cut 

 away from the body. Both cannulse are filled with serum, and 

 connected by india-rubber tubing to the ends of the tube c c' Q," , 

 care being taken to exclude air-bubbles. The end of the mano- 

 meter nearest c is filled with serum by opening the clip at Y, 

 and allowing all the air and a little serum to escape. The clip 

 is then replaced, and the heart allowed to beat once or twice, 

 with the stopcock c and the clip J freely open, so that it may 



o£ Blenheim Street, Oxford Street, has adapted a bobbin and rollers to the 

 revolving cylinder figured above, so that it will carry a continuous roll of paper, 

 and may be conveniently used instead of the kymographion shown in fig. 133. 

 The instruments which I have already described as necessary for experiments 

 may be obtained from him or from Oswald Hornn, Schiller Strasse, Leipzig. 



