NERVE 517 



lever and arrange to write on a slowly rotating drum. Place protected 

 electrodes from the secondary coil of the inductorium under the vpgal 

 trunk and remove the coil from the primary. Have the signal in the 

 primary circuit. Record a normal cardiogram, marking off exact ten- 

 second intervals. Now throw a weak alternating induction-current 

 through the electrodes, the signal marking the instant of stimulation. 

 The heart, after a latent period, stops in diastole. Note the length of the 

 latent period, and of the straight inhibition-line made by the heart- 

 lever. The viscus soon begins to slowly beat again and increases its 

 rate even though the alternating current be continued. The inhibitory 

 influence then is not complete, but only of a directing nature. Measure 

 the period of inhibition. 



Repeat this procedure with an induction-current stronger than the 

 one already used, then with a weaker one. The mode of inhibition will 

 vary according to the conditions. Observe that on resuming the beat, 

 the sinus venosus always begins first and the ventricle last. 



The six sorts of effect due to stimulation of the frog's cardiac inhibitory 

 nerves have been already given in Chapter VIII (see page 295) . 



Expt. 87. The Intracardiac Inhibitory Mechanism. (Apparatus: 

 Prog-board, inductorium, platinum electrode.) Pith a frog's brain. 

 Expose the heart and lift it up over with a glass rod. Find the whitish 

 crescent-shaped spot between the sinus venosus and the right auricle. 

 Here are situated the nerve-cells connected with the vagus. Stimulate 

 this "crescent" with the platinum electrode from the secondary coil of 

 an inductorium arranged for alternating currents. After a beat or two 

 the heart stops, but soon begins again despite continued stimulation. 



These nerve-cells (Remak's ganglion) situated in the crescent are the 

 inhibitory efferent nerve-cells; the corresponding efferent augmentor 

 cells are in the ganglia on the spinal roots part of the "sympathetic 

 system." They are probably the trophic centers of the heart in so far 

 as they determine the well-being of the fibers passing from them to the 

 cardiac muscle-tissue, for in a sense the well-being of any part depends 

 on the efferent fibers coming to its tissue. The nerve-cells in this gang- 

 lion have one, two, or many poles ; some of the unipolar cells in the frog's 

 septum have peculiarities, namely, "a spherical form, a pericellular net- 

 work, 'and two processes" the axis-cylinder and the spiral process 

 wound about the former. It is probable that this spiral process and 

 the pericellular net but not the axis-cylinder are in connection with the 

 vagus. (Retzius and Nikola jew). 



Expt. 64 demonstrated that the frog's heart apex containing no obvious 

 ganglion-cells could beat rhythmically. Perhaps then the inhibition 

 by these nerve-cells of Remak's ganglia is due to their quasi-trophic 

 influence over the heart's protoplasm. The matter is not certain. 



Expt. 88. Functions of the Hemispheres. (Apparatus : Decapitated 

 frog, sink full of cool water.) The frog, as given out, has had only the 

 cerebral hemispheres and the olfactory lobes anterior to them removed, 

 the optic thalami, cerebellum, medulla oblongata, and cord being struc- 



