THE ACTION OF INHIBITORY NERVES ON CARBON 



DIOXIDE PRODUCTION IN THE HEART 



GANGLION OF LIMULUS. 



By WALTER E. GARREY. 



{From the Physiological Laboratory of the Tulane University Medical School, New 

 Orleans, and the Marine Biological Laboratory, Woods Hole.) 



(Received for publication, September 18, 1920.) 



While stimulation of nerves generally results in increased activity, 

 the vagus has the opposite effect of diminishing the activity of the 

 heart. The mechanism of this inhibition has not yet been explained. 

 The author's recent experiments on the heart ganglion of Limulus 

 polyphemus^ have shown that stimulation of the inhibitory nerves of 

 this heart results in a decrease in the production of CO2 in the gang- 

 lion, while direct stimulation of the ganglion by electrical or mechani- 

 cal or chemical means has the opposite result, namely an increase in 

 CO2 production in the heart ganglion, as will be shown in a later paper. 

 This leaves no doubt that the action of the inhibitory nerves upon 

 automatic ganglia is due to a decrease in those chemical processes in 

 the ganglion which result in the formation of CO2. 



Methods. 



The rate of CO2 production was determined by the method previ- 

 ously described by the author. ^ Briefly, the ganglion, with its inhibi- 

 tory nerve is dissected from the heart and immersed in 3 cc. of a 



^ The special suitability of the heart ganglion of Limulus arises from the fact 

 that the heart may be isolated from the animal but beats for a day or more, 

 likewise the ganglion may be dissected free from the heart and if connected with 

 one segment alone will continue to deliver its impulses to the muscle for hours 

 in sea water or in the solution used in this investigation. We are thus able to 

 make our tests without concern about questions of changes of blood pressure, 

 of vasomotor action, of chemical composition of the medium, or of the secondary 

 action of other nerve supply which so complicate our experiments on the verte- 

 brate nerve centers. 



2 Garrey, W. E., /. Gen. Physiol, 1920-21, iii, 41, 49. 



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