PRACTICAL EXERCISES 



171 



Ventricular Contractions. (a) For this purpose two levers may be 

 arranged, one resting on the auricle, the other on the ventricle, the 

 writing points being placed in the same vertical straight line on the 

 drum. A convenient form of apparatus is shown in Fig. 61. 



(b) Gaskell's Method (a modification of). Attach a silk ligature to 

 the very apex of the ventricle. Divide the frgenum, cut the aorta 

 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 



FIG. 61. APPARATUS FOR OBTAINING A SIMULTANEOUS TRACING OF 

 AURICULAR AND VENTRICULAR CONTRACTIONS. 



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. 62). 



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 by cutting through the pectoral girdle in the way 

 described in 2 (p. 168). On clearing away a little connective tissue 

 and muscle with a seeker, three large nerves will come into view. 

 The upper is the glosso-pharyngeal, the lower the hypoglossal ; the 



