THE CAUSATION OF THE HEART BEAT 



1007 



One of the simplest methods is that devised by Gotch, represented in the diagram 

 (Fig. 451). The apparatus consists of a small glass jar with inlet and outlet tubes. 

 A disc of cork is fixed on to a brass rod so that it can be let down into the fluid. On 

 the upper end of the brass rod is poised a light lever with a paper point. To fix the 

 heart in the apparatus, the top of the ventricle is transfixed by a fine hook to which is 

 attached a thread connected with the lever. The heart is fastened to the cork by a pin 

 through the bulbus aortse. The glass jar is filled with the fluid whose action it is 

 desired to investigate. It is usual to start with Ringer's fluid in order to obtain a 

 normal, beat, and then to try in turn the various constituents of this fluid. 



FIG. 451. Gotch's frog heart apparatus. 



FIG. 452. Brodie's perfusion 

 apparatus for the mamma- 

 lian heart. 



Another method of investigating the action of the heart of cold-blooded animals is 

 by perfusing the heart cavities with the fluid under investigation. Two forms of 

 perfusion are made use of. In the method first introduced by Williams a double 

 cannula is tied into the ventricle, the rest of the heart being cut away. The tubes 

 leading to and away from the perfusion cannula are armed with valves so as to allow 

 the fluid to pass only in one direction. The contractions of the ventricle may be 

 recorded either by connecting the outgoing tube with a manometer, which may be a 

 mercurial or a membrane manometer, or by connecting some form of recording apparatus 

 with the vessel in which the heart is contained, so as to register changes in the volume 

 of the ventricle. A large number of different forms of apparatus have been devised 

 for these purposes. 



In another method the fluid is allowed to flow through the whole heart, passing in 

 by the sinus and out by the aorta. Here again the activity of the heart may be registered 

 either by recording the pulsations in the arterial column of fluid or by connecting a 

 tambour or piston recorder with the vessel in which the heart is contained. 



