SECRETION. 



471 



more disconnected from it ; until, in zoo- 

 phytes, we are scarcely able to distinguish a 

 nervous system at all, whilst all the operations 

 of* growth, nutrition, and secretion take place 

 very much as in plants, in which no nervous 

 system exists. Thus we find that " the ner- 

 vous system lives and grows within an ani- 

 mal, somewhat as a parasitic plant does in a 

 vegetable," deriving its nutriment from the 

 structure in the midst of which it is deve- 

 loped, and capable of exercising a certain ac- 

 tion upon it, but being strictly a superaddcd 

 part, and having rather an adaptive than an 

 essential connection with that structure. 



Now this view has derived from late dis- 

 coveries in minute anatomy, as complete a 

 confirmation as any such facts are capable of 

 affording. For it has been shown, not merely 

 that the functions of nutrition and secretion 

 are common to animals and plants, but that 

 the component elements of the organs by 

 which they are performed are in both instances 

 essentially the same. We have seen that the 

 act of secretion is effected, even in the most 

 complex gland, by the agency of aggregations 

 of ceils, each of which lives for and by itself, 

 and appears to be dependent upon no other 

 external conditions, than those which are re- 

 quired for the growth of the simplest cellular 

 plant, namely, food and warmth. And it is 

 difficult to conceive how, over that most es- 

 sential part of the secreting process the de- 

 velopement of the secreting cells the ner- 

 vous system can exert any direct influence. 



Another natural experiment, whose imme- 

 diate bearing is rather upon the physiology 

 of nutrition than upon that of secretion, but 

 which is really as conclusive in regard to the 

 latter as the former, is exhibited to us in the 

 early growth and developement of the em- 

 bryonic structure ; which makes considerable 

 progress, especially in invertebrated animals, 

 before any trace of the nervous system can be 

 detected. And in the human species the case 

 is not (infrequent, of the foetus coming to its 

 full size with the usual variety of textures in 

 its composition, but without either brain or 

 spinal cord. It has been said, however, that 

 in such instances the ganglia of the sympa- 

 thetic system probably exist, and supply the 

 influence supposed to be needed; but there 

 are cases on record, in which these would .seem 

 to have been carefully looked for and not de- 

 tected.* And moreover, even if their uni- 

 form presence were to be admitted, and the 

 power of sustaining the operations of nutri- 

 tion and secretion be supposed to reside in 

 them, how are we to explain the effects of in- 

 juries of the brain and spinal cord, the gangli- 

 onic centres being left intact ? We can see no 

 other consistent account of these phenomena, 

 than that which is presented by the last of the 

 three hypotheses enumerated ; the functions 

 of nutrition and secretion (like the contrac- 

 tility of muscular fibre) not being regarded as 

 dependent for their ordinary exercise upon 

 any power supplied by the nervous system, 



but being considered to be modified by causes 

 operating through it. 



And that this is the true view of the mat- 

 ter, would further appear from a careful exam- 

 ination into the nature of the phenomena 

 which folio 'v the section or injury of nerve- 

 trunks or centres, and which have been 

 supposed to indicate the impossibility of the 

 continuance of true nutritive operations after 

 the withdrawal of the hypothetical nervous 

 influence. In the first place, the effect pro- 

 duced by section of those nerves which are 

 supposed to exert the greatest influence, is 

 probably not in any ease a simple suspension 

 of the nutritive operations, nor a death of 

 the part ; but it is of the nature of inflam- 

 matory action, involving disordered nutrition 

 and perverted secretion. Further, this dis- 

 ordered condition does not seem to be the 

 direct result of the paralysis of the nerves, so 

 much as an indirect consequence of the want 

 of power to resist morbific causes. " It the 

 section of the sensitive nerves of a part," it 

 has been observed (with special reference to 

 the inflammations of the eye, the lungs, and 

 stomach, consequent upon section of the tilth 

 pair and par vagnm ), " were the direct cause of 

 its inflammation, we should expect to see in- 

 flammation in all parts of which tne sensitive 

 nerves are cut ; whereas the phenomenon in 

 question is seen only in a few parts ; and in 

 those parts it originates, and is chiefly seated, 

 in a single texture, viz. the mucous mem- 

 brane : that membrane is distinguished from 

 others in the body by its power of bearing the 

 contact of air, of foreign substances, and of 

 excretions elaborated within the body, with 

 impunity. This power seems obviously con- 

 nected with its vital power of throwing out, 

 when irritated, a mucous secretion, which 

 protects it equally as the cuticle protects the 

 true skin ; and this adaptation of the quantity 

 of protecting mucus to the irritation which 

 may act on a mucous membrane, may be very 

 naturally supposed to depend on its sensi- 

 bility, and to cease when its sensitive nerves 

 are divided, and allow the mucous membrane 

 to inflame and slough, equally as a serous 

 membrane would do {'rum the irritations 

 which, in the natural state, excite only a 

 healthy action upon it. On this supposition, 

 the inflammations in question depend, not 

 simply and directly on the division of nerves, 

 but on the action of the air, the food, the 

 bile, &c., on mucous membranes deprived of 

 their sensibility, and thereby in great measure 

 of their protecting mucus ; and bear an analogy 

 to the inflammations of the same membranes 

 which frequently take place from deficiency 

 of the mucous secretion, in cases of death by 

 starvation, and towards the close of lingering 

 and exhausting diseases.'" And lastly, even 

 supposing the inflammatory changes to be the 

 direct result of the paralysed state of the 

 nerves, they in themselves i.Hi>rd conclusive 

 evidence against the doctrine, that the nervous 

 influence is essential to the nutritive and 



Elber, de Acephalis, pp. 31. 35. 45. 



Brit, and For. Mod. Rev. vol. iii. p. 14. 



II H i 



