13 > EXPERIMENTAL PHYSIOLOGY 



CHAPTEK XIV 



DEMON STKATION OF THE MOVEMENTS OF THE MAMMALIAN HEART. 

 THE CARDIOGRAPH 



For the experiment a dog, cat, or rabbit is chosen, anaesthetised with 

 ether and morphia, and subsequently curarised by injecting a 

 solution of curare into the external jugular vein. Both vagi are 

 exposed, and ligatures passed round them through an incision in the 

 mid-line of the neck. The trachea is then isolated, and a Y-shaped 

 glass tube tied into its peripheral end. The heart is next exposed by 

 cutting through the sternum with bone forceps, keeping to the mid- 

 line as far as possible in order to avoid injuring any large blood vessel. 

 The thoracic walls are then drawn well apart, so as to thoroughly 

 expose the heart lying in the pericardium. 



As soon as the thorax is opened the lungs collapse and no longer 

 follow the movements of the thoracic wall. The animal would therefore 

 soon die of asphyxia, to prevent which it is necessary to supply it 

 artificially with air. This is done by rhythmically blowing up the 

 lungs through the trachea and then allowing them to collapse. 



There are many forms of apparatus which permit of this. A simple but 

 very effective arrangement is shown in fig. 109. A continuous blast of air is 

 obtained by the modified Bunsen pump, p. o is connected to a water tap, and 

 as the water is forced through the orifice at v, which nearly fills the con- 

 stricted neck of the outer receiver, air is drawn in through s. The mixture 

 of water and entangled air is collected in the large glass bulb, and the water 

 allowed to flow out through c. The supply of air is directed by a piece of 

 tubing, a, to the two-way tap t, whence it passes according to the position of 

 the tap along b to g, or, as represented in the figure, along the tube d to a 

 Woulffs bottle, h, containing some ether or other anaesthetic. It then passes 

 from f to g and thus to a coil of lead tubing, k, immersed in hot water, so that 

 the air is warmed to body temperature. Another piece of tubing connects it 

 to a Y-tube, one end of which, n, is tied into the trachea and the other is 

 covered with rubber tubing which can be partially compressed by the clip M. 

 The blast of air is made intermittent by either fixing a spring clip on L, which 

 is then opened and closed by hand, or the same residt is automatically effected 

 by the arrangement seen at R. This consists of a lever held down by two 

 springs so as to compress the tube against the base-board. The lever is 

 raised intermittently by an eccentric driven from the shafting. 



The blast of air is moistened in the pumn p. The force of distension of 



