302 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



the weight of the gland in saliva, even although, of course, the circulation 

 has been arrested. Then, again, the action of various drugs on the 

 salivary gland show the independence, to a certain degree, of the vaso- 

 inotor and secretory effects of the stimulation of the chorda tympani. 

 If fifteen milligrammes of atropine in solution are injected into the 

 jugular vein of a dog and the chorda tympani nerve then stimulated, 

 there is no flow of saliva, but, on examining the gland, the vaso-motor 

 phenomena which were present under the same circumstances before the 

 atropine was injected may be seen. In other words, vascular dilatation 

 follows stimulation of the chorda tympani nerve after the administration 

 of atropine, while the secretion of saliva is prevented. Then, again, by 

 means of pilocarpine the paralyzing effect of the atropine may be antag. 

 onized and the gland may be made to secrete. The dose of pilocarpine 

 which, when introduced into the general circulation, would be able to 

 remove the effects of atropine would probably be fatal to the animal. If, 

 however, the drug is allowed to enter the circulation of the gland, a 

 much smaller quantity will be efficient without danger to the animal. 

 Thus, if seventeen milligrammes of pilocarpine are injected into the sub- 

 maxillary duct after atropine poisoning and the chorda tympani then 

 irritated, a slight secretion will be produced, passing off again as the 

 stronger effect of the atropine makes itself felt. Then, again, the activity 

 of the secreting cells may be paralyzed, and the circulatory changes 

 produced by certain drugs, such as sodium carbonate in 5 per cent, 

 solution or hydrochloric acid in y 1 ^ per cent., injected into* the duct; but 

 as the increased pressure leads to trans udat ion, and as the cells cannot 

 secrete, oedema of the gland is rapidly produced when the chorda is 

 stimulated. Further, quinine injected into the duct influences vaso- 

 motor changes, although no secretion is produced even though the 

 secretory fibres of the chorda are not paralyzed. Evidently, then, the 

 chorda tympani nerve must contain two sets of fibres, the one vaso- 

 dilator, not paralyzed by atropine, and the other the secretory fibres, 

 paralyzed by that poison. It is only by the existence of a class of nerves 

 which act through calling into activit^y the protoplasmic energy of the 

 secreting epithelial cells that these effects can be explained. When the 

 chorda is irritated two sets of impulses travel along the nerve, one 

 impulse acting on the blood-supply of the glands, while the other acts 

 on the secretory elements of the epithelial cells in a manner analogous 

 to that which occurs when a motor nerve going to a muscle is irritated 

 the muscle contracts through the stimulation of the contractile elements 

 of the muscle-cells, and the blood-vessels dilate through vaso-motor influ- 

 ence. The result in both cases is probably of an electrolytic nature, 

 with the production of acid or alkaline decomposition products, and 

 these may serve as stimuli to the cells themselves, in the same way 



