[vincent-cameron] OBSERVATIONS ON VASO-MOTOR REFLEXES 269 



of the intestines, all cause a fall of blood pressure, under certain con- 

 ditions, and a rise under other conditions. These conditions we 

 believe are the same as for the corresponding results with the sciatic 

 nerve, though it is not always so easy to demonstrate this. 



The vaso-motor reflex from the ntestine is abolished by full 

 doses of nicotine, is reduced by section of the great splanchnic nerve 

 on both sides, and is abolished by extirpation of the semilunar ganglion. 



Our evidence in favour of the existence of vaso-dilator fibres in 

 afferent nerve trunks consists of results from certain animals in which, 

 no matter what the condition, with thorax opened, and curare ad- 

 ministered, stimulation of such nerve trunks resulted in a fall of blood 

 pressure, and secondly from the observations made during experiments 

 on the kneading of muscle, in which marked double-fall effects were 

 produced, easily traceable to separate causes: a vaso-dilatation and a 

 respiratory effect. 



Whether a rise or fall of blood pressure will result from stimul- 

 ation of an afferent nerve (terminals or cut central end) depends on 

 the relative effects of the three primary causal factors (a) reflex vaso- 

 dilation; (b) reflex vaso-constriction, and (c) frequency and depth of 

 resp ration, and the relative predominance of "one or more of these 

 factors is determined by (i) the strength of stimulus, (ii), the temper- 

 ature of the nerve, (iii) the anaesthetic, (iv) the degree of anaesthesia, 

 and (v) the idiosyncrasy of the animal. 



We beg to acknowledge the valuable assistance of Mr. John 

 Carmichael in all the experiments. 



Part of the expenses of this investigation has been defrayed by 

 a grant made by the British Association for the Advancement of 

 Science to the Ductless Glands Committee of the Association. 



