Active Hyperemia. 



387 



sign of vasodilation in the gland associated with secretin ; this is also seen 

 in some of the experiments of Barcroft and Starling (1904) on the gas 

 exchanges in the pancreas. Thus, during the normal rate of activity in 

 glandular organs, the metabolites are quickly removed and never reach a 

 high concentration. This is not the case with skeletal muscle where a 

 prolonged contraction compresses the blood vessels and banks up the 

 metabolites. Asher (1910), by means of minute doses of sodium fluoride, 

 was able to paralyse the secretory activity of glands without eliminating the 

 vaso-dilator response, from which he concluded that vaso-dilation could occur 

 independently of metabolites. 



The present investigation is an attempt to clear up these fundamental 

 problems : — 



a. To obtain evidence, if possible, for the undoubted existence of vaso- 

 dilator nerves. 



b. To determine the relative part played by metabolites and vaso-dilator 

 nerves in functional hyperaemia. 



c. If vaso-dilator nerves actually exist and are not an essential to functional 

 hyperaemia, what, then, is their function ? 



2. Methods. 



i. Measurement of vaso-dilation : a. direct blood flow ; 



b. indirect plethysmograph. 



ii. Estimation of metabolites : a. alkali reserve ; 



b. lactic acid. 



The preparation : The tongue, as pointed out by Anrep, possesses unique 

 advantages for the examination of these problems : the individuality of 

 function of its several nerves, which run separate courses, constituting an 

 easy and very certain means of determining the cause of hyperaemia. The 

 functional activity is almost purely muscular, since the total mass of lingual 

 glands is of comparatively insignificant amount. Dogs were found to be the 

 most convenient animals for these experiments which involved a good deal 

 of operative procedure, the accessibility of the structures in these animals 

 reducing injury to the tissues to a minimum. A preliminary dose of morphia 

 was given and complete anaesthesia maintained by means of chloroform and 

 ether ; in the few cases in which curare was injected decerebration preceded. 

 The lingual and hypoglossal nerves were exposed on both sides, and the blood 

 pressure was recorded in the femoral artery. 



Venous outflov: : A cannula was placed in the anterior transverse vein 

 connecting the two lingual veins, with ligatures and artery forceps so placed 



