376 



A TEXTBOOK OF PHYSIOLOGY" 



bloodvessels, arteries, capillaries, and veins, into a more rigid system, 

 through which a very rapid flow of blood takes place. Thus, the whole 

 gland swells under these conditions, and feels very tense to the touch. 

 If the blood-supply to the gland be lessened by a moderate compression 

 of its arterial supply, the rate of secretion remains unchanged. Con- 

 siderable compression decreases the amount. A salivary gland will 



i! Zaro 



SaJivary Zero 



rf-eri^l Zero 



Salivary Zero 



FIG. 193. TRACINGS FROM Two DIFFERENT DOGS, AN^ESTHETIZID in MORPHINE 

 AND CHLOROFORM, SHOWING THE ARTERIAL (CAROTID) PRESSURES AND THE 

 SECRETORY PRESSURES OF SALIVA DURING EXCITATION OF THE CKCEDA TYMPANI 

 NERVE. (From Proceedings Rcyal Society. ) 



With a salivary pressure of 240 mm. Hg and en arterial procure of ISO n.m. Hg., 

 . blood still flowed through the gland. 



even secrete a few drops when its blood-supply is cut off e.g., after 

 cutting off the head. Certain drugs, such as atropine, paralyze the 

 secretory fibres of the gland, but not the fibres producing vaso-dilata- 

 tion. Thus, when the chorda tympani nerve is stimulated after 

 injection of atropine, a rapid blood flow and increased pressure is 

 obtained in the gland, but no secretion. AH injection of quinine 

 hydrochloride produced vaso-dilatation in the gland, but no secretion. 



