178 GEORGE RALPH MINES, 



way as to restore the normal value of the P + of the blood. For this 

 is what happens in actual life. H 



The action of acids and alkalies on the heart was described by 

 Gaskell nearly thirty years ago. Let us note in detail the effects of 

 acid. Gaskell used lactic acid, but the description he gave of its action 

 on the heart applies equally to the effect of other acids, such as hydro- 

 chloric or even carbonic. The action on the heart is due to what 

 they have in common : an excess of the hydrogen ion. The essential 

 features of the action on the heart are these : The acid solution 

 diminishes the force of the systole, increases the diastole, and causes 

 arrest of the heart in a state of complete relaxation. If now the acid 

 solution is washed out with "neutral saline" (i.e. P+ about 6"5),* 



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 there is no recovery for some time, and then very feeble beats may 

 start. But if a slightly alkaline solution is used the recovery is 

 prompt, and the beats become as strong as at the start within a few 

 seconds, or at most in a minute or two. Further experiment shows 

 that the persistence of the after effect of the acid bears a definite 



relation to tlie P+ of the acid solution and to the duration of its 



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 application. With a minimal dose of acid applied for the shortest time 

 necessary to cause arrest of the heart, recovery on perfusion with 

 " neutral saline " may be fairly prompt and complete, but if the dose is 

 rather greater or applied longer the effect may persist for an liour or 

 more during subsequent perfusion with neutral saline. This is to be 

 regarded as the typical effect of acid on the heart. If the solution 

 is made too alkaline the heart is also stopped, but in this case in 

 systole. In the case of the frog's heart the divergence from neutrality 

 needed to produce the systolic alkaline arrest is much greater than that 

 needed to produce the diastolic acid arrest. Ptoughly, the limits are 

 about P+ 10 and P+ 5*5 respectively. It is not surprising then to 



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find that " neutral saline " restores the heart from the alkaline arrest 

 much more quickly than from the acid arrest, for this solution is much 

 nearer the " acid " limit than the " alkaline " limit. 



So far then we have these facts. The normal activity of heart muscle 

 (Jbij which we mean its power of giving automatic rhythmic contractions) 

 is possible only ivhen the hydrogen ion concentration of the solution in 

 contact with it lies within certain limits. If these limits are considerably 

 exceeded on the acid side, not only is the heart stopped, but some alteration 

 is imijressed on the muscle, ivhich is removed only very slovAy, if at all, by 

 a " neutral " solution, but instantly by an alkaline solution. 



* The slight deviation from strict neutrality is due to C0_. from the air. It is convenient 

 to use such a solution and it Avill maintain the heart-beat for hours. 



