470 



SECRETION. 



time when the real nature of the secreting 

 structure was altogether unknown, and when 

 the choice seemed to lie only between the in- 

 fluence of the nerves and that of the vessels, 

 it is totally fallacious now that a third agent 

 has been discovered, to which all analogy 

 would lead us to refer, at any rate, the chief 

 instrumentality in the operation. The prin- 

 cipal experiment adduced in support of this 

 hypothesis, and of the identification attempted 

 by Dr. Philip between nervous agency and 

 galvanism, was the effect of section of the par 

 vagum in checking the secretion of gastric 

 fluid, and the renewal of the process under 

 the influence of galvanism. We have already 

 shown the utter invalidity of this result as a 

 ground for any such inference; and it only 

 remains to show the inconsistency and insuffi- 

 ciency of the hypothesis itself, which is easily 

 done. For, as Dr. Prichard has justly re- 

 marked *, " if we begin by supposing the ex- 

 istence of the cause assigned, we shall find 

 that there is one agent, namely the galvanic 

 fluid, operating on one material, which is 

 the blood, and effecting its decomposition. 

 How. then, we may ask, does it happen that 

 so many different substances are, in different 

 examples of the same process, the results of 

 this single operation ? In other chemical de- 

 compositions, as when water is decompounded 

 by the galvanic fluid, the result is the same 

 and uniform. But in the instance supposed, 

 the operation of the same chemical agents 

 upon each other is followed by the formation 

 of products of the most different descriptions : 

 in one part of the vascular system the blood 

 is converted into bile ; in another, by the 

 operation of the same chemical agent, into 

 milk ; in another, into tears." This variety 

 of effects can only be explained by attribut- 

 ing them to the special endowments of the 

 several secreting organs through which the 

 nervous power is supposed to act ; and if it 

 be thus necessary to admit that such special 

 endowments do exist, by which the particular 

 nature of the secretion is determined, the 

 question naturally arises, Of what use is the 

 nervous power at all ? 



2. The second hypothesis, framed to meet 

 this objection, supposes, to use the language 

 of Prof. MUller, that " the influence of the 

 nerves on the glands merely enables the se- 

 creting substance, in each glancl, endowed with 

 peculiar properties, to exert its chemical ac- 

 tion." In order to sustain this hypothesis, it 

 is necessary to show that the processes of 

 secretion and nutrition are not only modified 

 by the division of the nerves by which their 

 organs are supplied, but that they are alto- 

 gether suspended by that operation ; the 

 secreting or growing structures having no 

 functional power of their own, save when 

 connected with certain nervous centres, which 

 are supposed to transmit to them the requisite 

 vital force : much as in a factory there may 

 be seen a great variety of machines, each of 



* Review of th Doctrine of a Vital Principle, 

 p. 198. 



them constructed to perform a certain special 

 action, but all of them dependent for their 

 power of carrying it into effect upon a general 

 motive power transmitted to each. We shall, 

 perhaps, more conveniently and satisfactorily 

 examine into the merits of this hypothesis, 

 by bringing it into comparison with the next. 



3. The third doctrine, of which Dr. Alison 

 has been one of the most philosophical and 

 consistent advocates, is to the effect that the 

 whole organic or vegetative life of animals, 

 i. e. every thing which goes on in them with- 

 out the intervention of any sensation or other 

 mental act, including the functions of nutrition 

 and secretion, may go on without the in- 

 tervention of the nervous system, and stands 

 in no relation of dependence to any changes in 

 nervous matter ; but that these changes exert 

 a powerful controlling and modifying influence 

 on the organic functions, increasing or dimi- 

 nishing their activity, or even altering their 

 character ; just as, to use the appropriate illus- 

 tration of Dr. John Reid, the movements of a 

 horse are influenced by the hand and heel of 

 the rider, although they are in themselves in- 

 dependent of him, being executed in virtue of 

 the power inherent in the animal. 



Now, in support of this last view of the 

 subject, it may be urged, in the first place, 

 that in one great division of the organised 

 world, namely, in the vegetable kingdom, the 

 functions of nutrition and secretion are per- 

 formed, not only independently of, but with- 

 out any kind of influence from, a nervous 

 system ; each act being the result of the pro- 

 perties inherent in the several parts of the 

 structure itself, called into play by the appro- 

 priate stimuli. We should have a right to 

 expect, therefore, that the corresponding func- 

 tions in animals should be adequately per- 

 formed by a similar mechanism ; and it is fair, 

 therefore, to throw the burthen of proof upon 

 those who maintain the contrary. If we fol- 

 low out in this case the great general principle 

 of Cuvier, which every clay's experience only 

 shows to be more strictly correct and more 

 widely applicable, that the different classes 

 of animals may be considered as so many ex- 

 periments ready prepared for us by nature, 

 who adds to or takes from their several 

 organs, just as we might wish to do in our 

 laboratories, showing us at the same time the 

 various results of these combinations, we see 

 that a comparison of different organisms 

 affords us a much better ground for the de- 

 termination of this question, than can be ob- 

 tained from the results of such experiments 

 as have been already cited ; it not being pos- 

 sible to make such experiments, without such 

 injury to the organism as is of itself a serious 

 disturbing cause. We notice, on looking at 

 the highest animal, that the organic functions 

 are brought into very close relation with the 

 animal powers, and are liable to be consider- 

 ably modified by the exercise of the latter. 

 But, as we descend the scale, we find the 

 nervous system constituting a less and less 

 predominant part of the organism, and the 

 apparatus of organic life becoming more and 



