DIGESTION 335 



itself possesses secretory fibres. So that, while there is no 

 doubt that the chorda tympani contains fibres whose function 

 is to increase the activity of the gland-cells, its vaso-dilator 

 action is, under normal conditions, closely connected with, 

 and, indeed, auxiliary to, its secretory action, although the 

 former does not directly produce the latter. This is only a 

 particular case of a physiological law of wide application, 

 that an organ in action in general receives more blood than the 

 same organ in repose, or, .in other words, that the tissues are fed 

 according to their needs. The contracting muscle, the secreting 

 gland, is flushed with blood, not because an increased blood- 

 flow can of itself cause contraction or secretion, but because 

 these high efforts require for their continuance a rich supply 

 of what blood brings to an organ, and a ready removal of 

 what it takes away. 



The quantity of blood passing through the parotid of a 

 horse when it is actively secreting during mastication may 

 be quadrupled (Chauveau). The parallel between the 

 muscle and the gland is drawn closer when it is stated that 

 electrical changes accompany secretion (p. 646), and that 

 the rate of production of carbon dioxide and consumption of 

 oxygen rises during activity. The temperature of the saliva 

 flowing from the dog's submaxillary during stimulation of 

 the chorda has been found to be as much as 1*5 C. above 

 that of the blood of the cartoid, although with the gland at 

 rest no constant difference could be detected (Ludwig). But 

 such measurements are open to many fallacies ; and while 

 there is no doubt that more heat is produced in the active 

 than in the passive gland, it will not be surprising, when the 

 vastly increased blood-flow is remembered, that no difference 

 of temperature between the incoming and outgoing blood has 

 been satisfactorily demonstrated, although we must assume 

 that such a difference exists. 



It has already been mentioned that most of the fibres of the chorda 

 tympani proper become connected with ganglion-cells, and lose their 

 medulla inside the submaxillary gland, only a few having already lost 

 it by a similar connection with ganglion-cells in the chordo-lingual 

 triangle. These facts have been made out by means of the nicotine 

 method previously described (p. 157). Thus, it is found that, after the 

 injection of nicotine (5 to 10 mg. in a rabbit or cat, 40 or 50 mg. in a 



