368 D. OGATA AND SWALE VINCENT 



With the increase of the strength of stimulus the respiratory 

 movements also increased, though not very markedly, and 

 therefore some of the falls following the rise on stronger stimu- 

 lation might have been more or less due to this complication. 

 But in the main it seems that the purely sensory nerves have 

 somewhat lower threshold than other kinds of nerves (fig. 10). 



Whether this is due to a large number of afferent fibers con- 

 ' tained in the sensory nerve than in those of the other kinds of 

 the same size could only be decided by more numerous experi- 

 ments and more elaborate methods than those we have employed, 

 as, for example, the measurement of resistance of each nerve 

 and more satisfactory methods of controlling the intensity of 

 stimulation in each case. 



In connection with the problem as to different kinds of nerves 

 we have studied the influence of the size of the nerve upon vaso- 

 motor reflexes. The hypothesis of Vincent and Cameron is 

 quoted at the beginning of this section. A similar problem was 

 taken up also by Stiles and Martin,^° who compared the effect 

 of stimulating two nerve paths at the same time with that of 

 exciting each by itself. They found that ''stimulation of two 

 afferent paths at the same time has often a more marked vaso- 

 motor effect than the stimulation of either path alone with an 

 equivalent strength of current. The degree of summation was 

 only moderate." This shows that the stimulation of a larger 

 number of afferent fibers will produce often a more marked 

 effect than that of few fibers. 



We stimulated two nerves of the same category but of different 

 sizes separately one after another under conditions as similar as 

 possible, a different number of afferent fibers being assumed to be 

 present in the nerves of different sizes. 



The results may be represented as follows, page 369. 



These few examples show that the results were not very con- 

 clusive. We can say only so far with some confidence that when 

 the responses were in the same sense, i.e., when the fall or the 

 rise was the result of corresponding equivalent stimulations, the 

 reflex change of blood-pressure was on the whole more marked 

 with the nerve of larger size than with those of smaller size (fig. 

 11). 



