174 GEOEGE RALPH MINES. 



great development,* the heart niuscle, and in particular that of the 

 thin-walled auricles and sinus venosus, is brought into very intimate 

 relation w^ith a constantly renewed layer of fluid. The stream of 

 fluid may be said to control the temperature and the chemical 

 environment of the cells. The efficiency of the perfusion method is 

 shown by the fact that with a suitable fluid the heart may be kept 

 beating regularly and strongly for many hours, while slight changes 

 in the composition of the perfused fluid with respect to an important 

 ingredient are followed by evident change in the character of the 

 beats within a very few seconds. 



As might be expected, the blood or serum from the animal whose 

 heart forms the subject of experiment forms a perfneion fluid effective 

 in maintaining the activity of the heart. But the classical researches 

 of Kinger revealed the all-important fact that these highly complex, 

 protein-containing solutions could be satisfactorily replaced (in the case 

 of the frog's heart) by certain solutions of simple inorganic salts. T^ e 

 presence of the inorganic salts of the serum in the fluid in contact with 

 the cells of the heart muscle is of more immediate importance for the 

 activity of these cells than is the presence of any organic food-stuffs. 

 It is true that it has been shown that the addition to the salt solution 

 of a small amount of glucose keeps the heart going for longer periods 

 than are attained without it ; and according to some the addition of 

 proteins has a beneficial effect, though this is denied by others who 

 have studied the point. The fact remains that with a solution of 

 simple inorganic salts in distilled water containing some dissolved 

 oxygen the hearts of various animals can be kept beating outside the 

 body for very many hours.f 



During this time, while the heart continues to contract regularly and 

 with sufficient force to enable it to pump through fluid with such 

 energy that if it were still connected to the arteries it could fulfil its 

 normal function of propelling fluid through the vascular system, and 

 while the frequency and form of the contractions remain essentially 

 like those observed in the heart of the uninjured animal, we may say 

 that the heart muscle is exercising its normal function, and although 

 the conditions are frankly abnormal in many respects, yet they 

 embrace those factors of environment which are immediately necessary 

 for the normal behaviour of the cardiac muscle cells. 



We must next consider what are the essential constituents of a salt 

 solution which will answer this purpose. 



* In mammalian hearts it is necessary to perfuse the coronary system, 

 t In working with the hearts of Elasmobranchs, as Baglioni (Zentralbl. f. Physiol. 19,385, 

 1905) showed, it is necessary to add urea to a neutral perfusion fluid. 



