Effect of Salts U pon the Invertebrate Heart. 245 



minutes contractions were resumed. At first these contractions 

 were very weak and of little amplitude, but they gradually became 

 stronger, and later diminished in the manner common to hearts 

 immersed in a pure solution of sodium chloride. 



The substitution of what is termed later in the paper the "opti- 

 mum solution" failed to restore rhythmic contractions in hearts 

 which had ceased beating in a sugar solution. 



A large number of experiments were made to discover if hearts 

 which had ceased beating in a pure NaCl solution could be made 

 to beat again by some other solution. In no case were beats 

 resumed after they had stopped in a pure NaCl solution. This 

 might seem to indicate that in this case irreversible compounds 

 are formed in the tissues of the heart under the influence of the 

 sodium chloride w^hich will not allow rhythmic activity to proceed. 



J. The Effect of Hydrogen Peroxide and of Oxygen in Solutions. 



During the course of the experiments it became evident that 

 in some cases at least the failure of the heart to respond to the 

 solutions was due to an insufficient supply of oxygen. Even when 

 well aerated the solutions contain less oxygen than does the blood 

 by which the hearts are normally surrounded. Lingle^ found 

 that the addition of small amounts of hydrogen peroxide to his 

 solutions aided very materially in the long continuance ot the 

 heart beats. My own experiences confirm his results in this re- 

 gard. In fact it seems safe to say that without a good supply of 

 oxygen the heart beats are impossible. 



In many experiments made with sodium chloride as the princi- 

 pal agent there was noticed a very marked loss of tone as the heart 

 continued to beat. At first this was attributed entirely to the 

 action of the NaCl but later it seemed more probable that the 

 loss of tone was, partly at least, due to the lack of oxygen. Hearts 

 beating in a solution lacking in oxygen show marked fatigue in a 

 short time and finally cease entirely to beat. Such hearts may 

 be revived and again caused to contract rhythmically by simply 

 adding to the solution in which the heart is immersed a little 

 hydrogen peroxide. The. following experiment will illustrate the 

 point in question: When a heart was immersed in what I have 



'Lingle. Loc. cit. 



