294 THE HUMAN BODY. 



through the secreting cells into the commencing ducts 

 as it passed through, dissolve out and carry on from the cells 

 the specific organic elements of the secretion. Of these, in 

 the submaxillary of the dog at least, mucin is the most im- 

 portant and abundant. That, however, the process is quite 

 different, and that there are in the gland true secretory fibres 

 in addition to the vaso-dilator, just as in the muscle there are 

 true motor fibres, is proved by other experiments. 



If the flow of liquid from the excited gland were merely 

 the outcome of a filtration dependent on increased blood- 

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

 tion 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 decapitated 

 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 question of 

 mere filtration, since a liquid cannot filter against a higher 

 pressure. Finally, the proof that the vascular dilatation is 

 quite a subsidiary phenomenon has been completed by show- 

 ing 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 nightshade, get similar phenomena 

 in the gland. In an atropized animal stimulation of the 

 chorda produces vascular dilatation 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 

 atropin 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 sympathetic 

 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 cer- 

 tain, 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 



