296 



ESSENTIALS OF PHYSIOLOGY. 



blood, and must be formed in the gland. (4) The pressure in the duct 

 of the gland during activity may be greater than the pressure in the 

 carotid artery, and therefore much greater than that in the capillaries 

 of the gland. (5) The molecular concentration of saliva in inorganic 

 salts is only about half that of blood, whereas if saliva were a nitrate 

 the concentration of salts would be the same as that of blood. (6) 

 Secretion may be obtained in the absence of blood. If the head of a 



FIG. 116. Effect of stimulation of the chorda tyrapani on the volume of the 

 submaxillary gland. (Bunch.) 



a, volume of gland ; 6, blood pressure. 



rabbit be cut off and the chorda stimulated immediately, a flow of 

 saliva is obtained. (7) The blood-vessels may be dilated without any 

 secretion taking place. In an animal to which atropine has been 

 administered stimulation of the chorda is followed by no secretion of 

 saliva, although the vessels become fully dilated. 



It has been suggested that, whereas the nervous factor undoubtedly 

 originates the salivary flow, other factors come into play to assist in its 

 continuance. Stimulation of the chorda is followed by a temporary 

 diminution in the volume of the gland, although the blood-vessels are 



