x VASCULAR MUSCLE AND NERVES 353 



of oue or other kind of vascular nerve. The dilators are more 

 readily excitable to currents of slow rhythm or low intensity ; 

 the constrictors, on the other hand, to tetanising currents, i.e. 

 currents of high frequency, or great intensity. These results 

 were strikingly developed and confirmed in the experiments of 

 Bowditch and Warren on the cat by the plethysmograph method, 

 in which the oscillations of volume in the hind -limbs were 

 recorded during the excitation of the sciatic by currents of high 

 or low frequency and intensity. The plethysniograms of Figs. 161 

 and 162 are so plain as to need no description. 



On the other hand, Piotrowski was unable on the dog to obtain 

 the same results as Bowditch and Warren. On stimulating the 

 sciatic with varying frequencies, he constantly observed a diminu- 

 tion and never an increase in the volume of the limb. 



The two kinds of vascular nerves, which run together in the 

 peripheral nervous system, may take a separate course at a higher 

 point and leave the cord at different places. This was shown by 



Fiu. 102. Plethysmograms of hind-limb of cat during electrical excitation of divided sciatic, by 

 induction shocks of equal frequency (1 per second), and equal duration (20"), but of varying 

 strength. (Bowditch and Warren.) At A, with strength of shock = 100, primary dilatation of 

 vessels of limb; at B, with strength of shock = 150, more pronounced dilatation preceded by 

 temporary contraction; at C, with strength of shock = 200, still more marked dilatation, 

 preceded by greater vascular constriction. 



Dastre and Morat, who, on exciting the thoracic sympathetic 

 immediately above the diaphragm, constantly obtained dilatation 

 of the vessels in the lower limbs, while on exciting the abdominal 

 sympathetic or sciatic they were constricted. 



Yet more interesting is another fact discovered by the same 

 authors, which plainly shows that the two kinds of vascular nerves, 

 running in a single nerve trunk, may supply quite distinct regions 

 at the periphery. On repeating the stimulation of the cervical 

 sympathetic (which forms with the vagus a single trunk, known as 

 the vago-synipathetic) on a curarised dog, they observed blanching 

 in the skin of the ear and rnucosa of the tongue, epiglottis, tonsils, 

 and soft palate on the side excited, with the simultaneous flushing 

 of the mucosa of the lips, gums, cheeks, hard palate, and nasal 

 mucosa on the same side. The effect is particularly striking on 

 comparison with the other side, and on contrasting the ischaemic 

 and hyperaemic parts. At the close of excitation the differences 

 gradually disappear, until the several parts regain their normal 

 colouring. The entire effect is due to the sympathetic alone, and 

 not to the vagus, since it appears when the sympathetic is excited 



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