360 



PHYSIOLOGY 



CHAP. 



arterial pressure, which varies with the pitch, strength, and timbre 

 of the sound, whereas in curarised animals the rise is hardly 

 perceptible (Dogiel). Lastly, both the number of sensory nerves, 

 and the extent of the area stimulated, have great influence on the 

 degree of pressor effect. For instance, on exciting a limited area 

 of the skin with strong chemical stimuli, with boiling water, or 

 red-hot iron, little or no rise of pressure is obtained ; on the other 

 hand, slight contact, tickling, or blowing of extended areas of the 

 skin, raises the arterial pressure to nearly double the normal 

 (Heidenhain and Griitzner). 



We saw in the preceding chapter that the central excitation of 

 the depressor nerves of Ludwig and Cyon invariably produces a 



Fir.. 106. Reflex lowering of arterial pressure of rabbit, from electrical excitation of 

 centripetal muscular nerve, in period comprised by vertical lines. (Tigerstedt.) 



marked reflex fall of arterial pressure (Fig. 165). The afferent 

 nerves to the muscles also constantly produce a similar effect on 

 blood pressure (Fig. 166). 



Few other afferent nerves are capable of producing reflex 

 depressor effects. The glosso-pharyngeal usually, but not invariably, 

 lowers blood pressure (Knoll). With mechanical stimulation of 

 the rectal and vaginal rnucosa, especially on touching the anus 

 and vaginal orifice, a primary fall of aortic pressure may be 

 observed on the curarised dog (Belfield). But if the stimulation 

 of the inucosa is pushed to deeper parts, the depression is less, 

 and may even be replaced by a pressor effect. Mechanical stimula- 

 tion of the skeletal muscles, again, may produce a depressor effect 

 (Kleen). 



We saw that the fall of arterial pressure consequent on excita- 

 tion of the depressors is due principally to the vaso-dilator fibres 



