THE CIRCULATION OF THE BLOOD AND LYMPH 139 



pressure. The same effect may be produced by fatigue or 

 cold, while heating a portion of the heart in general increases its 

 power of conducting the contraction. 



Chemical Conditions of the Beat. When we have localized 

 the essential mechanism of the rhythmical beat in the nervous 

 or in the muscular elements, the question may still be asked 

 what the chemical and physical conditions are which are 

 necessary to its maintenance. While it is known that a supply 

 of arterial blood at or near body-temperature, and under a 

 sufficient pressure, is required for permanent cardiac contrac- 

 tion, much simpler solutions will suffice to maintain the activity 

 even of the isolated mammalian heart for a considerable time. 

 One of the best of these is a solution containing sodium chloride, 

 potassium chloride, calcium chloride, and sodium bicarbonate 

 in the proportions in which they exist in blood-serum, with 

 the addition of a small quantity of dextrose (Locke). When 

 this solution, properly oxygenated and warmed, is circulated 

 through the coronary vessels of an excised rabbit's or cat's 

 heart, strong and regular beats may be observed for many hours. 

 Some investigators have claimed for sodium chloride, and even 

 for sodium ions, others for calcium salts or calcium ions, a special 

 role in the origination or maintenance of the rhythmical beat. 

 There is no doubt that strips from the ventricle of the tortoise 

 or turtle, which after isolation have ceased beating, and if left to 

 themselves in a moist chamber do not develop rhythmical con- 

 tractions, begin after a while to beat when immersed in or irri- 

 gated with a solution of sodium chloride or a solution of cane- 

 sugar containing a little of that salt. They refuse to beat in any 

 solution which does not contain sodium chloride (Lingle). The 

 addition of calcium chloride to the sodium chloride solution, or 

 preliminary treatment of the strip with a solution of a calcium 

 salt before its immersion in the sodium chloride solution hastens 

 the onset of the contractions, and increases the length of time 

 for which they are kept up (Erlanger) . It is unquestionable that 

 for the normal beat of the heart the presence of both salts is one 

 of the necessary conditions, but there is at present no sufficient 

 foundation for the view that either the one or the other acts as 

 a special chemical excitant of the automatic contraction. 



Resuscitation of the Heart. Not only can the beat of the 

 freshly-excised mammalian heart be long maintained by artificial 

 circulation, but many hours or even days after somatic death 

 pulsation may be restored by the perfusion of such a solution 

 of inorganic salts as Locke's through the coronary vessels. 

 Kuliabko in this way was able to restore a rabbit's heart which 

 had been kept forty-four hours in the ice-chest. Even after an 

 interval of three to five days from the death of the animal, in other 



