THE CARDIAC NERVES. 581 



suggested by Gaskell.* This author has shown that the after-effects 

 of stimulation of the inhibitory fibers are beneficial rather than in- 

 jurious to the heart ; that is, under certain circumstances an improve- 

 ment may be noticed in the rate or force of the beat or in the con- 

 ductivity. He has also shown, by an interesting experiment, that 

 during the state of inhibition the heart tissue is made increasingly 

 electropositive in comparison with a dead portion of the tissue. 

 To show this fact the tip of the auricle was killed by heat and this spot 

 (a) and a point at the base of the auricle (6) were connected with a 

 galvanometer. Under such conditions a strong demarcation cur- 

 rent was obtained flowing through the galvanometer from b to a. 

 If the auricle contracted a negative variation resulted, since during 

 activity b became less positive as regards a. If, on the contrary, 

 the auricle was inhibited by stimulation of the inhibitory fibers 

 a positive variation was obtained; b became more positive 

 toward a. On the basis of such results Gaskell concludes that 

 inhibition in the heart is due to a set of metabolic changes of an 

 opposite character to those occurring during contraction. In the 

 latter condition the metabolism is catabolic, and consists in the 

 breaking down of complex substances into simpler ones with the 

 liberation of energy as heat and work. During inhibition, on the 

 contrary, the processes are anabolic or synthetic and result in the 

 formation of increased contractile material whereby the condition 

 of the heart is improved. He would regard the inhibitory fibers, 

 therefore, as the anabolic nerve of the heart and their constant 

 action throughout life as an aid to the nutrition of the heart. The 

 same general view may be extended to all cases of inhibition, and 

 Gaskell believes that all muscular tissues are supplied with anabolic 

 (inhibitory) and catabolic (motor) fibers. t 



A more specific theory applicable to the case of the heart has been proposed 

 by the author. J In experiments made upon the isolated heart of the dog it 

 has been shown that during stimulation of the vagus potassium in diffusible 

 form is given off from tlie heart muscle (auricles). It is known that potassium 

 salts in a certain concentration in the circulating liquid will bring the heart 

 to a stand-still, and the state of potassium inhibition thus produced resembles 

 very closely the state of vagus inhibition. Since the vagus when stimulated 

 liberates potassium in a diffusible form, it is suggested that its action in 

 stopping the heart is effected through the agency of this substance. The 

 potassium exists in large percentage in the heart-muscle, but in a combined 

 form, and the theory assumes that the vagus impulses initiate a dissociation 

 or cleavage of some soi't which sets free some potassium in soluble form. ^ If 

 it is assumed that this liberation takes place in the part of the heart in which 



* Gaskell, "Philosophical Transactions of the Royal Society," London; 

 Croonian Lecture, part iii, 1882; "Journal of Physiology," 7, 46; and Meek 

 and Eyster, "American Journal of Physiology," 30, 271, 1912. 



t For a general discussion of this idea and of the importance of inhibitory 

 actions, see Melzer, "Inhibition," "New York Medical Journal," May 13, 

 20, 27, 1899. 



t Howell and Duke, "American Journal of Physiology," 21, 51, 1908. 



