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Rate of Beat of the Dog's Heart [Jan. 11, 



III. il The Direct Influence of Gradual Variations of Tempera- 

 ture upon the Rate of Beat of the Dog's Heart." By H. 

 Newell Martin, M.A., M.D., D.Sc, Professor in the Johns 

 Hopkins University, Baltimore, U. S. A. Communicated by 

 Dr. M. Foster, Sec. R.S. Received December 27, 1882. 



(Abstract.) 



In the investigations described, the method of experiment was such 

 as to completely isolate physiologically the heart of the dog from all 

 the rest of the body of the animal, lungs excepted. 



This was accomplished by occluding the right and left carotid and 

 subclavian arteries, the aorta just beyond the origin of the left 

 subclavian, and ligaturing both venae cava? and the azygos vein. In 

 consequence the only fraction of the systemic circulation left open 

 was that through the coronary system of the heart ; no organ but the 

 heart itself has any blood sent it, except the lungs. Hence the 

 cerebro-spinal nerve-centres and the sympathetic ganglia very soon die, 

 while the heart remains alive, in good working condition, for two hours 

 or more. The right auricle is supplied uniformly with defibrinated 

 calf s blood, conveyed to the superior vena cava from Marriotte flasks. 

 The blood, after traversing the pulmonary circuit, is finally pumped 

 by the left ventricle into a cannula, which is tied into the aorta just 

 beyond the origin of the left subclavian artery. From the distal end 

 of the cannula a wide rubber tube carries the blood to an exit cannula 

 seven or eight feet above the level of the heart. By raising or lower- 

 ing this exit, and by raising or lowering the level of the Marriotte 

 flasks feeding the heart, arterial and venous pressures could be 

 changed at will, or maintained very nearly constant. 



Venous and arterial pressures being kept constant, the temperature 

 of the blood supplied to the heart was gradually changed by raising 

 or lowering the temperature of the water contained in the vessels in 

 which the feeding Marriotte flasks were immersed. 



The pulse rate was recorded by a Fick's spring manometer, and 

 arterial pressure by a Marey's mean-pressure mercury manometer, 

 each being connected with the central stump of a carotid artery. 

 Temperatures were read by means of a thermometer tied into the root 

 of the left subclavian, so that its bulb projected into the aortic arch. 



Uniform artificial respiration was maintained. 



As the result of many experiments it was found (1) that the isolated 

 dog's heart beats quicker when supplied with warm blood, and slower 

 when cold blood is supplied to it ; (2) that the rate of beat depends 

 much more upon the temperature of the blood in the coronary 

 arteries than on its temperature in the right auricle or ventricle ; (3) 

 that when defibrinated calf's blood is used to feed the heart that organ 



