FUNCTIONS OF THE CEPHALIC NERVES. 177 



mucous and watery secretions was much less than usual, although obvious 

 marks of inflammation were present. In order to avoid error as much as pos- 

 sible, Dr. Reid made five sets of experiments, employing two dogs in each, as 

 nearly as possible of equal size and strength, introducing the same quantity of 

 the poison into the system of each in the same manner, 'but cutting the Vagi 

 in one, and leaving them entire in the other. This comparative mode of 

 experimenting is obviously the only one admissible in such an investigation. 

 Its result was in every instance opposed to the statements of Sir B. Brodie ; 

 the quantity of the mucous and watery secretions of the stomach being nearly 

 the same in each individual of the respective pairs subjected to experiment; 

 so that they can no longer be referred to the influence of the Eighth pair of 

 nerves. Moreover, the appearances of inflammation were, in four out of the 

 five cases, greatest in the animals whose Vagi were left entire ; and this seemed 

 to be referable to the longer duration of their lives after the arsenic had been 

 introduced. The results of Sir B. Brodie's experiments may perhaps be ex- 

 plained, by the speedy occurrence of death in the subjects of them,consequent 

 (it may JDC) upon the want of sufficiently free respiration, which was carefully 

 guarded against by Dr. Reid. 



2*37. So far as the results of Dr. Reid's experiments may be trusted to, 

 therefore, (and the Author is himself disposed to rely on them almost impli- 

 citly,) all me arguments which have been drawn, in favour of the doctrine that 

 secretion depends upon nervous agency, from the effects of lesion of the Vagi 

 upon the functions of the stomach, must be set aside. That this nerve has an 

 important influence on the gastric secretion, is evident from the deficiency in 

 its amount, soon after the operation, as well as from other facts. But this is a 

 very different proposition from that just alluded to; and the difference has 

 been very happily illustrated by Dr. R. " The movements of a horse," he 

 observes, "are independent of the rider on his back; in other words, the rider 

 does not furnish the conditions necessary for the movements of the horse ; but 

 every one knows how much these movements may be influenced by the hand 

 and heel of the rider." It may be hoped, then, that physiologists will cease 

 to adduce the oft-cited experiments of Dr. Wilson Philip, in favour of the 

 hypothesis (for such it must be termed) that secretion is dependent upon 

 nervous influence, and that this is identical with galvanism. Additional evi- 

 dence of their fallacy is derived from the fact mentioned by Dr. Reid, that the 

 usual mucous secretions of the stomach were always found ; and they are fur- 

 ther invalidated by the testimony of Miiller, who denies that galvanism has 

 any influence in re-establishing the gastric secretion, when it has been checked 

 by secretion of the nerves. 



238. It only remains to notice the influence of section of the Vagi upon the 

 actions of the Heart. It has been already stated that mechanical irritation of 

 these nerves, especially at these roots, has a tendency to excite or accelerate 

 the heart's action. It remains to inquire, if its movements are dependent upon 

 their influence ; or if these nerves form the channel through which they are 

 affected by emotions of the mind, or by conditions of the bodily system. In 

 regard to the first point, no doubt can be entertained, since the regular move- 

 ments of the heart are but little affected by section of the Vagi. With respect 

 to the second, there is more difficulty, since the number of causes which may 

 influence the rapidity and pulsations of the heart, is very considerable. For 

 example, when the blood is forced on more rapidly towards the heart, as in exer- 

 cise, struggling, &c., the stimulus to its contractions is more frequently renewed, 

 and they become more frequent; and when the current moves on more slowly, 

 as in a state of rest, their frequency becomes proportionabry diminished. If 

 the contractions of the heart were not- dependent upon the blood, and their 

 ttumber were not regulated by the quantity flowing into its cavities, very 



