272 THE HUMAN BODY* 



the outcome of a filtration dependent on increased blood- 

 pressure in it, then it is clear that the pressure of the- 

 secretion in the duct could never rise above the pressure in 

 the blood-vessels of the gland. Now it is found, not only 

 that the gland can be made to secrete in a recently decapi- 

 tated animal, in which of course there is no blood-pressure, 

 but that, when the circulation is going on, the pressure of 

 the secretion in the duct can rise far beyond that in the 

 gland arteries. Obviously, then, the secretion is no ques- 

 tion of mere nitration, since a liquid cannot filter against a 

 higher pressure. Finally, the proof that the vascular dila- 

 tation is quite a subsidiary phenomenon has been com- 

 pleted by showing that we can produce all the increased 

 blood-flow through the gland without getting any secretion 

 that just as in a muscle nerve we can, by curari, paralyze 

 the motor fibres and leave the vaso-dilators intact, so we 

 can by atropin, the active principle of deadly night-shade, 

 get similar phenomena in the gland. In an atropized 

 animal stimulation of the chorda produces vascular dila- 

 tation but not a drop of secretion. Bringing blood to 

 the cells abundantly, will not make them drink; we must 

 seek something more in the chorda than the vaso-dilator 

 fibres some proper secretory fibres; that the poison acts 

 upon them and not upon the gland-cells, is shown, as in 

 the muscle, by the fact that the cells still are capable of 

 activity when stimulated otherwise than through the 

 chorda tympani. For example, by stimulation of the sym- 

 pathetic fibres going to the gland. 



So far then we seem to have good evidence of a direct 

 action of nerve-fibres upon the gland-cells. But even that 

 is not the whole matter. It is extremely probable, if not 

 certain, that there are two sets of secretory fibres in the 

 gland-nerves : a set which so acts upon the cells as to make 

 them pass on more abundantly the transudation elements 

 of the secretion (the water and mineral salts), and another, 

 quite different, which governs the chemical transformations 

 of the cells so as to make them produce mucm from mucigen 

 previously stored in them, in a way comparable to the pro- 

 duction of trypsin from trypsogen in the active pancreas. 



