196 



THE CIRCULATION OF THE BLOOD AND LYMPH 



across close to the bulbus, pinch up a tiny portion of the auricle and 

 ligature it. Remove the intestines, liver, lungs, etc., care being taken 

 in cutting away the liver not to injure the sinus. Then remove the 

 lower jaw, and cut away the whole of the body except the head, part 

 of the oesophagus, and the tissue connecting it with the heart. Fix 

 the head in a clamp sliding on an ordinary stand. The heart is held 

 at the auriculo-ventricular junction in a Gaskell's clamp supported on 

 a separate stand. The thread connected with the ventricle is brought 

 round a pulley and attached to a lever above the heart. The auricle 

 is connected with another lever. The writing-points of the two levers 

 are arranged in a vertical line on the drum. The small pulley must 

 be oiled from time to time to lessen the friction (Fig. 90). 



If tortoises or turtles are available, the much larger heart of these 

 animals may be used for Experiments 5 (2) (a) and (&). The animal 

 having been killed by cutting off its head, the ventral portion of the 

 carapace is detachc d by the saw. The pericardium can now be slit 

 open, and the pads of the levers arranged on auricles and ventricle 



fad fo rest an Aurtcte 

 / . Pad to rest on Ventrtcte 



Fig. 89. Apparatus for obtaining a Simultaneous Tracing of Auricular and 

 Ventricular Contractions. 



respectively, as in Experiment 5 (2) (a), without further disturbing 

 the heart. Or the heart may be removed, together with the upper 

 portion of the body, the pericardium opened, and the liver cut away. 1 

 The aortic trunk is then divided, and the portion of it attached to 

 the heart grasped by a small forceps clamp. Fine silk ligatures are: 

 attached to the apex of the ventricle and the top of the right auricle.. 

 The vagus nerves are exposed in the neck, ligated, and divided. The 

 upper portion of the body is supported on a stand. The forceps grasp- 

 ing the aorta is fixed in an ordinary holder, and the threads are attached 

 to the levers, as in Experiment 5 (2) (b). 



With the vagi, Experiment 7 may be performed. It must be remem- 

 bered that the activity of the two vagi is unequal in the tortoise, the 

 right being the more active. 



6. Dissection of the Vagus and Cardiac Sympathetic Nerves in the 

 Frog. (i) Put the tissues in the region of the neck on the stretch by 

 passing into the gullet a narrow test-tube or a thick glass rod moistened 

 with water, and by pinning apart the anterior limbs. Expose the heart 



