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/Vv'/.V(Y/Y./:\V OH GENERAL PHYSIOLOGY 



made by llrid Hunt (1H97), who found that the result on the heart beat of 

 simultaneous stimulation of the vagus and accelerator nerves was nil or minimal, 

 if the effects when separately stimulated were equal and opposite. If the 

 stimulation of the one was interpolated in the middle of that of the other, the rate 

 of the beat was brought back towards that of the normal. In other words, the 

 nerves are purely antagonistic and " the statement that a minimal stimulation of 

 the one can completely overcome a maximal stimulation of the other is undoubtedly 

 incorrect." 



On the other hand, the experiments of von Frey (1876) are sometimes quoted 

 in support of the opposite view. These experiments showed that, on maximal 

 stimulation of chorda tympani and sympathetic nerves at the same time, the rate 

 of blood flow througli the submaxillary gland was slowed, showing that the 

 constrictor effect overpowered the dilator one. When the stimulation ceased, the 

 dilator effect of the chorda tympani showed itself to last longer than the constrictor 

 effect of the sympathetic. By appropriate choice of the relative strength of the 

 stimulation of the two nerves, Asher (1909) showed, however, that the effect of either 

 dilator or constrictor nerves can be made to preponderate. Anrep and Cybulski 



\ M 



FIG. 116. POSITIVE VARIATION OF THE DEMARCATION CURRENT OF THE FROG'S 

 VENTRICLE IN CONSEQUENCE OF STIMULATION OF THE VAGUS. 



One electrode leads off from an injured sjx>t. 

 String galvanometer. 



Upper tracing the monophasic electrical changes. The tops are too high to be included on the plate. 

 Below it reference line. 



Lower tracing spontaneous heart beats, recorded by a lever. 



On stimulation of the vagus, marked by the signal, there is a gradual fall in the diastolic level of the 

 galvanometeil ine ; that is, there is an electrical effect in the opposite direction to that associad <l 

 with contraction. After this effect has passed off, there is a temporary rise in the level of the 

 diastolic position of the string. Note that the diastolic position of the lever marking the beats 

 shows no alteration during the course of the vagus inhibition. 



(After Samoilov.) 



(1884) found it easy to make either effect show itself in the case of the tongue. 

 It is to be noted that von Frey's experiments were made to test a particular 

 hypothesis, that of interference in ganglion cells, and the results are not in 

 disagreement with the view of the supply of the same individual muscle fibre by 

 two separate nerve fibres of opposite action. 



Secretion. If the view taken in our chapter on Secretion be correct, namely, 

 that, up to a certain stage, this process is an automatic one on the part of the cell 

 mechanisms, there is some reason to suppose that there might be nerves inhibiting 

 the process. In the case of the pancreas we have met with some evidence, brought 

 forward by Pavlov and his co-workers, that the vagus nerve contains inhibitory 

 fibres for this gland. One way in which this influence can be seen is the 

 following : suppose that we have, by repeated periods of stimulation of the vagus, 

 obtained a flow of juice; this flow outlasts the actual period of stimulation, and, 

 if the stimulation be applied to the vagus afresh before the effect of the preceding 

 stimulation has ceased, it will be seen that the first effect is a cessation of the flow, 

 which is afterwards followed by an increase. The reader may remember that this 

 is very similar to the phenomenon seen in the action of the same nerve on the 



