76 



EXPERIMENTAL PHYSIOLOGY 



made to include all the remaining structures of the neck except the trachea. 

 The head is cut off by an incision in front of these ligatures passing between the 

 occiput and atlas. Oozing of blood is stopped by application of dilute supra- 

 renal extract, and the skin is fastened over the cut end of the neck. Before 

 tying the arteries, a tube has been inserted into the trachea, and artificial 

 respiration kept up by pumping air into the lungs and allowing it to escape by a 

 side tube. This air is warmed, and the body is further kept warm after decapi- 

 tation by placing it on a warmed plate and covering it with cotton-wool. In 

 such a preparation the circulation is maintained, although the pressure is some- 

 what low, and the tissues continue to live for several hours. Spinal reflexes can 

 be studied in it (see Chapter XXV.). The heart is exposed by severing four or five 

 ribs or rib-cartilages on each side by bone forceps, and with the same instrument 



FIG. 63. DIAGRAM OP MAREY'S CARDIOGRAPH, a, RECEIVING TAMBOUR FOR FIXING OVER APEX- 

 BEAT ; 6, RECORDING TAMBOUR CONNECTED WITH, a, BY RUBBER TUBING, WITH A LATERAL 



OPENING CLOSED BY A CLIP. 



cutting through the sternum near its lower end, and raising the detached part 

 forcibly, along with the cut ends of the ribs. This bony and muscular flap may, 

 if necessary, be removed altogether after tying a string or wire tightly round its 

 anterior end to arrest bleeding from the internal mammary arteries. The window 

 thus opened discloses the heart within the pericardium ; the latter may be cut 

 open and the heart fully exposed. The systole, followed by diastole, of auricles 

 and ventricles can be watched, and the hardening of the ventricles during their 

 systole felt by applying the finger to their surface. By attaching one of the 

 ventricles and one of the auricles by fine hooks and threads to light levers 

 suspended by rubber threads, the contractions of these parts can be recorded 

 separately on a drum. The effect of stimulating the vagus in the neck and of 

 atropine in abolishing this effect can be demonstrated ; also the effect of stimu- 

 lating the accelerator fibres which pass from the inferior cervical ganglion of 

 the sympathetic to the cardiac plexuses. The same effect is obtained by 

 stimulating the ganglion itself, which may be found by following the cervical 

 sympathetic downwards. (In the cat the vagus and sympathetic run in the 

 same sheath in the neck, but they separate below and above as the sym- 

 pathetic passes out of and into its inferior and superior cervical ganglia.) 



