CIRCULATION. 189 



has become accustomed to the new solution before making an observation. The 

 heart should, as a rule, be constantly supplied with fresh fluid, as in the natural 

 state. The resistance against which the heart works is also a factor of import- 

 ance. The water with which the solutions are made should be distilled in glass, 

 as the minutest trace of the compounds of heavy metals in non-colloidal solu- 

 tions affects the heart. 1 



Nutrient Solutions. — Cyon found that the beat of the extirpated frog's 

 heart is very dependent on the nature of the solution with which the heart is 

 fed. Hearts supplied with normal saline solution (NaCl, 0.6 per cent.) ceased 

 to beat much sooner than those left empty. The serum of dog's blood seemed 

 almost poisonous. Rabbit's serum, on the contrary, postponed the exhaustion 

 of the heart for many hours, provided the limited quantity contained in the 

 apparatus was renewed from time to time. Serum used over and over again 

 caused the beats to lose force after an hour or two. The renewal of the serum 

 seemed a stimulus to the heart, causing it to contract very strongly during a 

 half minute or more, after which the contractions became less energetic. 



Cyon's immediate successors, Bowditch, Luciani, and Rossbach, confirmed 

 his observations. None of these investigators, however, was concerned pri- 

 marily with the nutrition of the heart. The first systematic work on this sub- 

 ject was done, as has been said, by Meruuowicz, who attempted to maintain 

 the beat of the heart with normal saline solution containing various quantities 

 of blood, with normal saline alone, with a watery solution of the ash of an 

 alcholic extract of serum, and with a normal saline solution containing a 

 minute amount of sodium carbonate. The direction taken by him has been 

 pursued to the present day, the chief objects of study being the importance to 

 the heart of sodium carbonate or other alkali, sodium and potassium chloride, 

 the salts of calcium, oxygen, proteids and some other organic bodies such as 

 dextrose, and, finally, of fluids possessing the physical characteristics of the 

 blood. The outcome of this work we must now consider. 



The value of an alkaline reaction has been generally recognized. Sodium 

 carbonate is the alkali commouly preferred. The favorable influence of this 

 salt probably does not depend on any specific action, but simply upon its 

 alkalinity. The alkali promotes the beat of the heart by neutralizing the 

 carbon dioxide and other acids formed in the metabolism of the contracting 

 muscle; this, however, may not be its only use. 



Certain of the salts normally present in the blood are necessary i" main- 

 tain the beat of the heart. Sodium chloride is one of these. The solution 

 employed should contain a " physiological quantity." Such a solution is said 

 to be " isotonic." The amount required t<» make a sodium chloride solution 

 "normal" or " isotonic" for the frog is <).(> per cent., for the mammal Dearly 

 1 per cent. Enough of a calcium salt to prevent the washing ouf of lime 

 from the tissues is also essential for prolonged maintenance of the contractions. 

 A heart fed with normal saline solution is before long brought t<> a stand ; the 

 addition of a calcium salt to the solution postpones the arrest. The character 

 'Locke: Journal of Physiology, lK'.t.">, xviii. p, 331. 



