136 APPENDIX 



Obs. 5. Cat's heart is as suitable as rabbit's, but requires a larger supply of fluid. A heart 

 from a preparation lost by MgSO^ inflow in an a. p. exercise still serves for perfusion 

 experiment. 



Experience shows that for most students a somewhat difficult part of the exercise is in 

 the excision of the heart, frequent causes of failure being wounding of the heart, or rough 

 handling of it, or extreme slowness in the procedure of removal, with resultant patchy clots 

 in the coronary system. An occasional source of failure is the insertion of the aortic 

 cannula too low or too far down into the aorta, so that the nozzle of the cannula blocks the 

 orifices of the coronary arteries or renders incompetent the aortic valve. The perfusing 

 fluid then enters the ventricle instead of perfusing tlie coronary vessels. For the purposes 

 required here the rabbit is killed preferably about 5'-10' before the dissection is to be begun, 

 and by the method used in provision for exerc. I. 



In the perfusion apparatus it is important to keep the stalk of the Y-piece, attached to 

 the vertical perfusion-tube, short, and to secure it firmly with a cork in the upper neck of 

 the warm-water jacket (condenser tube), and thus prevent unsteadiness of the heart cannula 

 when the beating heart hangs from it. 



Obs. 6. Should the heart have failed, by over-heating, after the first part of the exercise, 

 it may happen that a decapitated cat-preparation serving for some other exercise at another 

 table is by this time finished with : the heart from it can then furnish the second part of 

 this perfusion experiment, as it will have become practically free from the CHOI3 with 

 which it was originally dosed. 



Obs. 7. The ' warming of the pace-maker ' part of the exercise, though simple and rather 

 rough in method, provides an observation of interest and theoretical importance and works 

 reliably. 



EXERCISE III 



A purpose of this exercise is to afford the student further practice in carrying out the 

 quick removal of the heart without injury to it. It is the removal of the heart which seems 

 to present the main difficulty to the student. 



Obs. 9. Ether may be preferred to CHCI3 as more akin to modern surgical practice ; in 

 that case an appropriate concentration is given by 1 c.c, ether per litre Einger-Locke. It 

 should be freshly prepared ; it loses concentration more rapidly than the CHCI3 solution. 



EXERCISE IV 



1. Instruments required hy the student. In addition to the instruments brought with 

 him, the student is supplied at his place (for two students) with the retracting-clips, bent 

 mounted needles, thread and cotton, small artery-forceps, mug of Ringer-Locke over 

 midget Bunsen, eye-holed bent packing-needle and string, inductorium, voltaic cell, bridge- 

 keys and wires, and hand-electrodes, as mentioned above, pp. 130-1, The packing-needle 

 should be not too large and have been curved freely in the flame close behind its eye-holed 

 point. It serves for passing the string for occluding the intercostal arteries when ligating 

 the ribs and the internal mammaries when ligating the sternum, A large strong-bladed 

 pair of scissors is provided for cutting the ribs. The voltaic cell is conveniently placed 

 on the lower shelf of the operation table, the inductorium on the upper. The above 

 set of instruments are supplied similarly for all the exercises succeeding this one. 



