THE CIRCULATION OF THE BLOOD. 299 



In potassium chlorid solutions isotonic 0.9 per cent. with sodium 

 chlorid solution the heart strip also fails to contract. This is the case also 

 when the potassium is added to the sodium chlorid in amount practically 

 equal to that found in the blood. 



2. On the Mammalian Heart. The collective action of the inorganic 

 salts on the isolated heart of all members of this class of animals which have 

 been made the subject of experimentation, is as marked, if not more so, than 

 it is on the heart of the frog or terrapin especially when the coronary blood- 

 vessels are perfused with Ringer's solution or the modification of it suggested 

 by Locke, as follows: NaCl 0.90 per cent.; CaCl 2 0.024 per cent.; KC1 0.042 

 per cent.; NaHCO 3 0.02 per cent., dextrose o.i per cent. The reviving and 

 sustaining power of this solution is extraordinary. Locke and Rosenheim 

 were able to revive the isolated heart of a rabbit and to excite it to active 

 contraction, for several hours at a time, on four consecutive days by perfusing 

 it with this solution saturated with oxygen and at a temperature of 35 C. 

 No special precautions were observed other than keeping it cool (10 C.) and 

 moist during the intervals of experimentation. The duration of the irrita- 

 bility and contractility extended over a period of 95 hours. Kuliabko 

 revived the heart of a rabbit for an hour nearly three days after removal from 

 the body of the animal. It was then placed on ice, and after four days it 

 was again revived by perfusing it with Ringer's solution. Altogether this 

 heart retained its irritability for seven days. Hering revived the heart of a 

 monkey on three different occasions, the first, 4^ hours, the second, 28 

 hours, and the third 54 hours after the death of the animal. In the inter- 

 vening periods the heart was also kept on ice. In this animal it was even 

 possible to increase and decrease the activity of the heart by stimulation of 

 the nerves which normally control the rate of the beat. Kuliabko was also 

 able to revive the isolated heart of a child 20 hours after death from a double 

 pneumonia. It was made to beat rhythmically at a rate varying from 70 to 80 

 per minute when the solution had a temperature of 39 C., and at a rate of 

 98 to 102 per minute when it had a temperature of 41 C., though at this tem- 

 perature the beat became arrhythmic. All these instances demonstrate the 

 extreme persistence of the irritability of the heart-muscle under appropriate 

 conditions. 



The action of individual salts has been shown experimentally on the 

 hearts of rabbits, cats, dogs, monkeys, by Gross, Howell and others. Thus 

 it has been found that when an isolated heart is rhythmically beating in 

 response to the perfusion of Ringer's or Locke's solution, the addition of 

 potassium chlorid in small amounts is followed by a decrease in the rate and 

 force of the contraction, and in larger amounts by a complete cessation of the 

 contraction and a standstill in diastole. On the withdrawal of the potassium, 

 the former frequency and vigor are regained. Potassium exerts a depressor or 

 an inhibitor influence on the irritability and contractility of the heart- 

 muscle. 



Under the same conditions, the addition of calcium chlorid in sufficient 

 amounts is followed by an increase in the rate and in the vigor of the con- 

 tractions; on its withdrawal both rate and force return to the previous condi- 

 tion. Calcium exerts an accelerator and an augmentor influence on the 

 irritability and contractility of the heart. 



