THE CIRCULATION OF THE BLOOD. 243 



a convenient elevation. The lever is allowed to write on a moving drum, and 

 serum is passed through at various temperatures. After a short time the heart 

 may stop beating ; but two wires are arranged, the one in the canula, the 

 other projecting from the plate in such a way that the heart can be moved 

 against them by shifting the position of the bell- jar a little. The wires act as 

 electrodes, and can be made to communicate with an induction apparatus, so 

 that single induction shocks can be sent into the heart to produce contractions, 

 and if need be, by means of the trigger key, at one definite point in the revo- 

 lution of the recording cylinder. 



Electrical Phenomena of the Heart-beat. The phenomena of 

 the natural beat of the heart are generally considered to indicate that 

 the systolic contraction is a single and not a tetanic one. The electrical 

 changes support this view. During the contraction a distinct electrical 

 change occurs which is similar to that which happens in skeletal muscle 

 with each contraction. It has been demonstrated that a stanniused 

 frog heart undergoes two changes or phases as regards its electrical con- 

 dition, the first immediately before the contraction, in which the excited 

 part becomes negative to the other parts, contraction following the 

 wave of excitation, and the second during relaxation, in which the cur- 

 rent flows in an opposite way. 



The Metabolism of the Heart. Whatever view may be taken of 

 the nature of the rhythmic cardiac contractions, it will be generally 

 acknowledged that the contractions cannot long be maintained without 

 a due supply of blood or of a similar nutritive fluid. Some very re- 

 markable facts have been made out about this, in the case of the frog's 

 heart. For instance, it has been shown that normal saline solution is 

 insufficient to maintain the contractions, and that in experiments in 

 which it is necessary to maintain the beats for any length of time failing 

 serum or saline solution of dried blood, the solution should contain 

 some serum-albumin, and that there should also be present some potas- 

 sium chloride, and Dr. Ringer has composed a nutritive fluid which 

 contains chlorides of sodium, potassium, and calcium in small amounts, 

 which is able to maintain the normal beats of the heart. It is therefore 

 very reasonable to suppose that the amount and quality of the blood 

 supplied to the human heart has the greatest influence in maintaining 

 the force and frequency of the rhythmic activity. The view that is 

 taken at present of the action of the heart is one propounded by Gaskell, 

 viz., that in heart muscle as in protoplasm generally, the metabolic pro- 

 cesses are those of anabolism or building up, which takes place during 

 the diastole of the heart, that vagus stimulation helps on this process, 

 and of catabolism or discharge, which is manifested in the contraction 

 of the heart, and which is accelerated by stimulation of the sympathetic 

 fibres. That vagus stimulation is therefore ultimately beneficial to the 

 contractions. The electrical currents set up on the stimulation of the 



