SECRETION OF SALIVA. 227 



placing bull dog forceps on the two ducts well forward of the point 

 where the lingual crosses them. This causes the ducts to distend 

 and into the one which does so most markedly a small cannula is 

 inserted by the same manipulation as for a vein (p: 8d). 



The skin wound should now be carried back and the sub- 

 maxillary gland carefully freed by blunt dissection from the neigh- 

 bouring tissues, care being taken not to injure the veins. The 

 exposed gland should be kept moist with warm^todke's solution. 



The cannula is connected by suitable rubber tubing with a bent 

 glass tube so arranged that the drops of secretion may fall from its 

 free end. Having ascertained the rate of secretion (by counting the 

 drops) for a normal period of one minute the chorda is stimulated 

 for a few moments with a feeble interrupted current. When the 

 secretion has returned to normal, stimulation is repeated with a 

 stronger current. 



The relationship between the response and the strength of the 

 stimuli should be carefully noted. Those near the preparation can 

 usually see that the gland becomes flushed and apparently swollen 

 by the stimulation, this effect being usually most pronounced during 

 the first-applied stimuli. What conclusions are warranted from 

 the results? The observations are repeated during stimulation 

 of the central end of the vago-sympathetic in the neck. 



The secretion pressure is now measured by connecting the 

 cannula, by moderately thick-walled, but yet flexible tubing, with a 

 mercury manometer, the tubing being filled with physiological 

 saline. The carotid blood pressure is also observed, and it is 

 advantageous to arrange the writing styles of the two manometers 

 so that they write in the same perpendicular on a drum. When the 

 chorda is stimulated with a current which gives a maximal secretion, 

 the pressure in the duct manometer steadily rises until it overtops 

 that in the artery. Explain the significance of this result. 



The manometer is now removed, and, through a cannula pre- 

 viously inserted in the femoral vein, 10-15 mgm. of atropine sul- 

 phate dissolved in physiological saline is injected. When the drug 

 has developed its full action on the heart (how is this tested?) the 

 chorda is again stimulated with a maximal current, and the effect 

 on the secretion and the vascularity of the gland observed. What 

 has been the action of the atropine? Of what significance is the 

 experiment? 



