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A TEXTBOOK OF PHYSIOLOGY 



The vaso-dilator nerves for the limbs issue in the posterior spinal 

 roots. The posterior roots contain the afferent nerves (touch, pain, 

 etc.). The same fibres serve as vaso-dilator fibres. The impulses 





FIG. 120. DIAGRAM OF A PLETHYSMOGRAPH AND PISTON RECORDER. 

 The rubber bands fasten the glass lid in position. 



which produce vaso-dilatation are termed " antidromic " (against 

 the stream). We know that nerve fibres conduct impulses indifferently 

 in either direction, and that the synapsis and nerve endings control 

 the result of such impulses. 



FIG. 121. PITHED CAT: CAROTID BLOOD-PRES^TEE. (H. II. Dale.) 



Upper curve shows effect of 025 milligramme of adrenalin tefore, lower curve o 

 O'l milligramme of adrenalin after, 10 milligrammes of crgotoxine. 



Excitation of these posterior roots causes reflexly a rise of blood - 

 pressure, and directly a vaso-dilatation in the part the nerves supply. 

 Thus it is assured that the irritated or injured part receives immedi- 

 lately a greater supply of blood. 



