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MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. X, NO. 3. 



period of time. In using this apparatus the pressure upon the heart can be varied by elevating 

 the bottles A and R and the resistance to the systole by elevating the drip tube II. We have 

 found in practice that the elevation to the bottles and to the drip tube must have such relation 

 that the drip tube\shall be at least as high as the pressure point in the bottles. 



Our experience shows that in order to get the best results with this apparatus some care and 

 experience are necessary in so adjusting the height of the reservoir bottles above the heart that 

 the amount of pressure upon the heart during diastole and the amount of resistance to the heart 

 during systole shall be properly proportioned to the size and power of the organ. In the frog, 



Fig. 3. 



and probably other reptiles, the internal diastolic cardiac pressure is very slight, so that in the 

 isolated heart it is very easy to have conditions, both during diastole and systole, which are 

 entirely unnatural. " 



" In trials with the pure Kinder solution as a nutrient fatigue developed so rapidly as, in our opinion, to make 

 trustworthy results impossible. The fluid which we finally used was similar to that originally employed by Williams, 

 except in the substitution of bullocks' for rabbits' blood. Our fluid consisted of a mixture of one part of defibrinated 

 bullocks' blood to two parts of a half per cent of saline solution. In order that the heart might have a constant 

 supply of oxygen, in no case was the same blood passed twice through the heart. In one of the large reservoir 

 bottles was placed the pure nutrient fluid, in the other nutrient fluid containing the required percentage of alcohol, 

 so that by simply changing the clip, without altering the pressure or in any way disturbing the heart condition, 

 pure nutrient fluid or alcoholized fluid could be run through the viscus at will. We had some difficulty in working 

 the Williams valve until our dinner, suggested the use of the skin of the frog, which we found when used fresh or 

 even after keeping in saline solution would do admirably. 



