332 PHYSIOLOGY CHAP. 



electrical phenomena that accompany the inhibitory processes, 

 and are the converse of those concomitant with the accelerator 

 processes. 



The intact and the resting heart are iso-electric. When any 

 point of the walls is injured, or excited, by any cause, that point 

 becomes <>alvanometrically negative in relation to the intact, or 

 inactive, parts : and on connecting the injured, or active, point 

 with any other intact, or inactive, point, a current known as the 

 demarcation, or action, current passes through the galvanometer 

 (Hermann). 



Now Gaskell has shown that if the heart of a tortoise is 

 arrested by the upper Stannius ligature, and the tip of the auricle 

 killed with hot water, then on leading off the demarcation current 

 to the galvanometer, and exciting one of the branches of the vagus 

 (running with one of the coronary veins from the sinus venosus 

 to the auriculo-ventricular groove), a positive variation, i.e. an 

 increase of the demarcation current, is apparent. Since this effect 

 cannot be due to increased (gal vanome trie) negativity of the 

 dead point, we must assume that it is the result of augmented 

 (galvanometric) positivity of the intact part. We must therefore 

 conclude that excitation of the vagus in a resting heart produces 

 modifications of its metabolism, expressed in an electrical variation, 

 opposed to that which occurs in the contraction of cardiac muscle. 



According to Gaskell, the altered metabolism produced by 

 vagus excitation consists in an increase of reparatory or anabolic 

 processes ; while the stimulation of the sympathetic fibres accelerates 

 the disintegrative or katabolic processes. The action of the vagus , 

 is therefore diastolic because it promotes anabolic processes, while 

 that of the sympathetic is systolic because it promotes the katabolic 

 processes. The probability of this theory is attested by the fact 

 that vagus excitation is followed by a phase of increased activity 

 as its after-effect, showing that the cardiac muscle is strengthened, 

 not weakened, while, on the other hand, excitation of the sym- 

 pathetic is followed by breaking-down, consumption, and exhaustion 

 of the myocardium (Gaskell). The anabolic action of the vagus 

 is, as we have seen, associated with diminished reflex excitability 

 of the cardiac muscle (negative bathmotropic effects), so that the 

 latter on direct stimulation no longer reacts by a contraction, save 

 when the stimulus is excessive. This fact explains the mechanism 

 of active diastole, as determined by the vagus ; it is the effect of 

 the lowered excitability of the myocardium, by which systole is 

 hindered, and diastolic expansion of the muscle cells promoted. 



Other facts described at different times by various authors 

 harmonise with Gaskell's theory (which Fano was the first to 

 bring forward in Italy). Panum and Giannuzzi observed on the 

 rabbit that weak stimulation reinforced a previously weakened 

 cardiac activity. Traube noticed that on interruption of artificial 



