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The Relation between Secretory and Capillary Pressure. I. — The 



Salivary Secretion. 

 By Leonard Hill, F.B.S., and Martin Flack (Eliza Ann Alston Besearch 

 Scholar). 



(Beceived April 23,— Bead June 20, 1912.) 



(From the Physiological Laboratory of the London Hospital Medical College, London 

 Hospital Eesearch Fund.) 



Since Ludwig made the discovery that the secretory pressure of a gland 

 may double that of the arterial pressure when the outflow of saliva is 

 obstructed, no one, so far as we know, has investigated the circulatory 

 conditions in the gland under these circumstances. This has been the object 

 of the present research.* Our method is as follows : — We place a cannula in 

 the duct of the submaxillary gland of the cat or dog and prepare the chorda 

 tympani nerve for excitation. A second cannula is placed in the carotid artery 

 of the opposite side of the neck. Each cannula is connected, either with a 

 mercurial manometer or, as in our latest experiments, with two Leonard 

 Hill pocket sphygmometer gauges. This gauge consists of a thick-walled 

 glass tube with a fine capillary lumen closed at one end where the lumen 

 expands into a small air chamber. Half an inch from the open end there is 

 a side hole. On placing this end in a solution of potash a fluid meniscus rises 

 to the side hole, which marks the zero of the instrument. (Potash is used to 

 keep the tube free from grease.) One end of a piece of rubber is slipped over 

 the open end of the gauge so as to cover the side hole, and the other end then 

 connected with the cannula. The pressure of the saliva or blood forces the 

 meniscus up the gauge, which is graduated in millimetres of mercury and acts 

 as a spring manometer. We find these gauges very convenient to use as they 

 can be placed side by side and the readings compared at a glance. Before 

 making the connections with the gauges we expose the veins which course 

 over the submaxillary gland and contribute to the formation of the external 

 jugular vein. Having found the vein which issues from the gland we 

 tie all the other veins, leaving this one free so that at the right moment 

 we can clip the external jugular and open it so as to observe the outflow of 

 blood from the gland. When all is thus prepared we excite the chorda 

 tympani nerve. As soon as the secretory pressure rises above the arterial 

 pressure we open the vein and observe the flow of blood. We find that under 



* Towards the expenses of this research a grant was made by the British Medical 

 Association. 



