VASOMOTOR REFLEXES 357 



were obtainable by varying the rate of stimulation from 1 to 20 

 stimuli per second. This was later incidentally confirmed by 

 Hunt.i« 



Thus, for the investigation of the complicated problem of 

 vasomotor reflexes, it became very necessary to investigate each 

 possible factor separately. In this way only would one be able 

 to answer correctly for the normal vasomotor response. 



The present investigation was undertaken for the purpose of 

 studying some of the factors separately, of confirming previous 

 investigations, and of trying, if possible, to reconcile contradic- 

 tory views as to the conditions which determine any particular 

 vasomotor response. 



We beg to acknowledge our indebtedness to Mr. John Car- 

 michael for his valuable assistance in all our experiments. 



2. THE INFLUENCE OF RESPIRATORY MOVEMENTS UPON BLOOD- 

 PRESSURES 



It is well known that the respiratory center can easily be 

 affected by central stimulation of sensory nerves. Thus HowelP* 

 writes in his Textbook of Physiology that ''stimulation of any 

 of the sensor}^ nerves of the body may affect the rate or the 

 amplitude of the respiratory movements. ' But no mention is 

 made of the influence of these movements upon blood-pressure. 

 The same applies to other text-books, except Starling's,^^ in 

 which we find, ''The increased respiratory movements will also 

 aid the venous' circulation and have a similar effect in increasing 

 the systolic output," which would necessarily bring about a rise 

 of blood-pressure. But, "A constant and immediate result of 

 exaggerated respiratory movements is a fall of blood-pressure," 

 and not a rise, as Vincent and Cameron pointed out. They 

 found that "the extent of the fall of pressure appeared to be at 

 any rate largely proportional to the violence of the respiratory 

 activity," that the fall of blood-pressure was "brought about by 

 performing rapid artificial respiration by compression of the 

 thorax," that "deep voluntary breathing in the case of the 

 human subject produced a regular and pronounced lowering of 

 the blood-pressure," that "the more widely the thorax is opened 



