THE CARDIAC NERVES. 521 



existence in the body of definite nerve fibers with apparently the 

 sole function of inhibition, it seems appropriate in this connection 

 to refer to the views regarding the nature of this process. Several 

 general views of the nature of inhibition have been proposed, but 

 the one that is most definite and has met with most favor is that 

 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. f 



The heart muscle possesses a motor (accelerator) as well as an 

 inhibitory nerve. They exercise opposite effects upon the heart 

 muscle, and this result finds a satisfactory provisional explanation 

 in Gaskell ? s hypothesis, just stated. But the further question arises 

 as to why they should have opposite effects. Is it due to a differ- 

 ence in the character of the nerve impulses they carry or is it due to 



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

 Croonian Lecture, part in, 1882; also " Beitrage zur Physiologie," dedicated 

 to C. Ludwig, 1887 ; and " Journal of Physiology," 7, 46. 



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

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

 20, 27, 1899. 



