VASOMOTOR REFLEXES 361 



Therefore we do not conclude that such a fall of blood-pressure 

 is always produced by increased respiratory movements. But 

 the important point for us at present is the undoubted fact that 

 increased respiratory movements can and do cause a fall of 

 blood-pressure, and that this fall can be easily eliminated by 

 opening the thorax sufficiently wide. 



These observations, along with various others quoted above 

 from the paper by Vincent and Cameron both on animals and 

 on human subjects, confirm fully their statement as to the occur- 

 rence of a fall of . blood-pressure brought about by increased 

 respiratory movements, and probably explain the nature of this 

 fall. We believe that the increased respiratory movements 

 caused by sensory stimulation form a very important com- 

 plication which has often led to misunderstanding of the true 

 vasomotor reflexes. 



Gruber and Kretschmer, as mentioned before, deny this re- 

 spiratory effect upon blood-pressure. They used a slow rate of 

 stimulation and the fall of blood-pressure was the usual effect. 

 But the fall is generally thought to be a result of weaker stimu- 

 lation, and they do not deny that the increased respiratory 

 movements to a certain degree cause a fall of blood-pressure 

 when the stimulus is strong enough as to produce them. 



Our experiments were made on thirty- three dogs. 



3. THE EFFECT OF THE STRENGTH OF THE STIMULUS UPON 



VASOMOTOR REFLEXES 



After repeated experiments by numerous investigators, the 

 generally accepted view as to the effect upon the vasomotor 

 reflexes of different strengths of stimulus seems to coincide with 

 Knoll's^^ original statement, i.e., that a depressor effect is usu- 

 ally the result of a weak stimulation, while a pressor effect fol- 

 lows, as a rule, a stronger stimulation. Reid Hunt^* pointed out 

 that weak stimulation was one of the methods of obtaining a 

 reflex fall of blood-pressure, and Vincent and Cameron noticed 

 the same fact. 



Among more exhaustive investigations on this point we should 

 refer to those by Porter,29-34 Martinj-^-^^.^o and their respective 



