268 THE ROYAL SOCIETY OF CANADA 



pronounced fall. Respiratory movements are markedly increased, 

 and the extent of the fall appears to be largely proportional to the 

 violence of the respiratory activity. During the actual stimulation 

 there is either a very slight rise, or a more marked rise, or the pressure 

 remains about constant, while the fall usually begins at the moment 

 of cessation of the stimulation. There is thus a clear indication of 

 the action of two opposing influences, a reflex vaso-constriction, pro- 

 ducing a rise, and violent respiration, producing a fall. 



A similar fall of pressure is brought about by performing rapid 

 artificial respiration by compression on the thorax, and can be in- 

 duced in the human subject by rapid and deep voluntary respiration. 



The effects so far described (except the last) apply to animals 

 anaesthetised with ether, and the same are generally true if chloro- 

 form, chloral hydrate, or urethane are employed. When the animal 

 is under the influence of morphia, electrical stimulation of the central 

 end of the sciatic produces a rise of pressure, while mechanical 

 stimulation of the skin produces a fall, but there is every reason to 

 believe that this is after all a quantitative, and not a qualitative differ- 

 ence. It is difficult to apply a mechanical stimulation to the skin 

 which can be considered as the equivalent of a rapidly interrupted 

 electrical stimulation upon the sciatic. 



When the animal is fully under the influence of curare, stimulating 

 the central end of a cut nerve trunk invariably causes a rise of blood 

 pressure. This effect seems to be due, largely at any rate, to the 

 cessation of respiratory movements. 



The more widely the thorax is opened, the more does the fall of 

 blood pressure obtained by stimulation of nerve tend to become re- 

 placed by a rise (animal under ether). The lowering of blood pressure 

 when the central end of the sciatic nerve has been stimulated, as also 

 when rapid artificial respiration has been performed by compression 

 of the thorax, and further also when rapid and deep voluntary res- 

 piration is performed upon human beings, is probably due to direct 

 mechanical influence upon the heart's action, or interference with the 

 return of blood to the heart, or both. 



The result of a weak stimulation is usually a fall of blood pressure, 

 while a pressor effect follows as a rule a stronger stimulus (confirm- 

 atory of Knoll and of Hunt). The difference however we have not 

 observed when the thorax is opened. 



Cooling the nerve tends to produce vaso-dilator effects (confir- 

 matory of Howell, Budgett and Leonard, and of Reid Hunt). This 

 also we have been unable to observe in an animal with the thorax 

 opened. 



Stimulation of the skin, kneading of muscle, and manipulation 



