398 



Mr. D. T. Harris. 



similar to the vasodilation produced by stimulation of the lingual nerve 

 (compare figs. 17 and 6) and by the normal metabolites arising from muscular 

 activity (compare figs. 17 and 4). Lactic acid, directly or indirectly, is 

 therefore a true vaso-dilator substance. 



• 



6. Functional Hyperemia. 



We must now arrive at a decision regarding the mechanism by which the 

 vaso-dilation accompanying muscular activity is brought about. Let us 

 consider the first possibility, viz., that some form of reflex excites the vaso- 

 dilator nerves into action at the same time as or soon after the stimulation 

 of the motor nerve. 



In glandular organs, the vaso-dilator fibres run in the same bundle as the 

 secreto-motor fibres (e.y., the chorda tympani to the submaxillary gland) and 

 do not admit of direct analysis ; the attempt to block one or other by means 

 of drugs is not as convincing as simple section. 



In our preparation, however, it is the vaso-constrictor fibres which run with 

 the motor nerve while the fibres with a vaso-dilator action are bound up in the 

 separate sensory nerve ; we are thus enabled, by means of section, to interrupt 

 any reflex arc (unless it be a peripheral axon reflex) through which vaso- 

 dilation might be produced during motor activity. 



An examination of the accompanying plethysmographic records (figs. 18 

 and 19) shows that as the initial mechanical stimulation of the lingual nerve 

 (fig. 7) passes off, the vaso-dilation produced by faradisation of the hypoglossal 

 nerve gradually becomes as great after as before section of the lingual nerve. 



(LiTTgtuiZs cut) 



Fig. 18. 



Division of the motor nerve makes no difference to the form of the curve, 

 the same degree of dilation being produced by stimulating the uncut nerve 



