CHAP. II. which it is immediately preceded, we find its knowledge not as yet to III. THE have been ascertained,(g) though of late it has, with great probability of ESSENTIAL accuracy, been ascribed to electricity occasioned by the contact of the nerves with the muscles.(r) PROPER- Treating of the uses of the Nervous System, and of Sensitiveness and Contractility, Dr. Bostock seems to admit, that they are not essential to mere vitality, because, he says, that without them man would be a mere automaton without homogeniety and destitute of consciousness, from which it would be inferred, that, though sensation and contractility may be indispensable to perfection, yet that life might continue without them.(s) Certain peThere are certain peculiar and extraordinary powers and properties culiar pow- incident to vitality, which should here be noticed. The first requisite ers or pro- involved in the name and notion of an organized body, is a determinate perties of vitality. form, designed for certain ends. That species, therefore, of the vital powers is most general, which produces the genital and nutritive fluids, and prepares them for organic nature, and which have been denominated by Blumenbach the Nisus Formativus, because it is the source of all generation, nutrition, and reproduction,(t) and by which power, lacerated, or fractured parts are reproduced.(u) of new, and power of The perpeNo point in physiology is better settled than that, although the body tual change remains apparently the same, yet its component parts, however solid, are of parts and subject to perpetual mutation.(x) The component particles of all the formation structures, even of bone itself, undergo a slow but constant change, and after a temporary sojourn, some parts are taken away and carried back restoring again into the circulating mass, to make way for other new parts to be lacerated deposited in their place. The absorbent vessels (principally the lymparts or phatics) effect this purpose, and are subsidiary to the process of nutribroken tion and growth;(y) in other words, the particles of which the body is bones. composed have a tendency to change; the old ones are perpetually removed, while fresh matter is continually deposited in their place.(z) As long as life lasts, the fluids are subjected to a constant internal motion, in which we can trace evidence of an uninterrupted separation of old particles, and a correspondent admission of new ones; and though the form of the body remains the same, its component parts are subject to perpetual mutation. These changes necessarily imply that the fluid parts are constantly being converted into solid structures, to maintain their growth and nutrition, and, again, that the particles which had for some time formed part of the solids, are taken up by the absorbent vessels and carried back into the current of the circulation, to make way for the new matter about to be deposited in their stead.(a) (9) 1 Bost. 192, &c.; and see post as (r) See post, 44, 45; and 3 Bost. 281. (s) 1 Bost. 207. (t) El. Blum. 29, 62. By this power we know that the claws and parts of lobsters and crabs are reproduced, and parts of worms, when separated, will reunite. 3 Bost. 53. (u) See 1 Bost. 99; post, as to bones; 3 Bost. 271. (x) Quain's Elem. Introduc. 18; 2d edit. 20, 21; 1 Bost. 101, 102; 2 Bost. 152; id. 99, 423; see post, under the absorbent function, as to the office of the lymphatics. (y) Id. ibid.; and see 5 Good, 168, 176; El. Blum. 382, 383; 2 Bell's Anat. 336 to 343; Cooper, Dict. tit. Absorption; Amer. Cyclop. Prac. Med. tit. Absorption. But note, it is considered that the brain, the spinal chord, and the organs of sense, undergo less of this exchange of particles than other parts. 2 Bost. 431, note. (z) Crawford on Animal Heat, 150; 2 Bost. 99. (a) 2 Dunglison, 165, &c. PROPER &c. This renovating power extends to the bones as well as to every other CHAP. II. part;(b) and it has been observed, that we have reason to suppose, that, III. THE every portion of bone, like every other organized part, is connected both ESSENTIAL with the arterial and the absorbent systems, and that, in process of time, TIES, each particle is removed, and fresh ones deposited in their place. This gradual exchange of old for new matter, is proved by the phenomena which attend the growth of bone. A solid organized body cannot grow by the distension of its parts, or by the accretion of new matter to its external surface, but by the gradual remodelling of the whole. If the secreting vessels be supposed to act more powerfully than the absorbents, the new matter is either conveyed more rapidly or in greater quantity than the old matter is removed, so that the bulk of the whole is ultimately increased, and yet the operation is effected so gradually, that the general form of the bone, and the relation of its different parts to each other, are not materially altered.(c) Hence it has been observed, that a bone itself exhibits very unequivocal marks of vitality.(d) This renovating power also extends to the Nerves, which are not only repaired but even reproduced; and after a nerve has been completely divided, and its functions totally suspended, it has been known gradually to resume its power, and the ends were found to be connected by the formation of a new substance.(e) Dr. Roget has written a beautiful article upon Age, in which he has ably illustrated this doctrine, and stated, that doubts may very reasonably be entertained as to the identity of any part of the body, at different epochs of its existence. A period of seven or eight years was assigned by the ancients as the time required for this entire change of all the materials of the system; but Dr. Roget observes, that modern researches, which show us the much more speedy reparation of injured parts, and the rapid renewal of the substance of bones that have been tinged by madder given to animals with their food, render it extremely probable that a complete renovation takes place in a much shorter period.(ƒ) This constant motion and renewal of new materials, partly composed of or influenced by the powerful antiputrescent gastric juice associated with the animal heat, unquestionably tend to prevent the decomposition and putridity that would otherwise ensue, and contributes to the duration of vitality.(g) Self-adjustment is also an important feature in the animal economy, Self-Adand one which materially affects its operations and regulates its motions, justment. which have been characterized by the term Self-Adjustment.(h) Exposed as the body is at all times to a variety of external agents, differing from each other both in their direct and their indirect effect, it was necessary that there should be some kind of corresponding change in the machine, to prevent the irregularities that might otherwise arise in its action. Now, we shall find, that the different vital functions are so adapted to each other, that their respective defects or excesses are compensated by the extraordinary action of some other function, and which is the necessary result of the previous irregularity. It was from observing a number of examples of this kind, that a pathological hypothesis was formed, which has long been a favourite doctrine of the schools of medicine, according to which all these trains of action are referred to the (b) 1 Bost. 101 to 105. (c) 1 Bost. 101, 105, 259, 260. (d) Id. ibid.; Convers. Animal Econ. 124. (e) 1 Bost. 360. (f) Cyclop. Med. Prac. tit. Age, 35; (h) 2 Bost. 147. CHAP. II. operation of a specific principle, which has been named the vis medicaIII. THE trix naturæ, but upon which Dr. Bostock has judiciously observed, that ESSENTIAL there is no foundation for this mode of reasoning, as these trains of acPROPER- tion can be referred to no one physical principle, and only agree in their final cause. They resemble each other only in exhibiting examples of the admirable order which pervades all parts of the universe, and which we observe as well in the inanimate as in the animated parts of the universe.(i) TIES, &c. Reaction. Secondly, tractility. Reaction. There is also another peculiar operation confined to the living body, and which tends to preserve the machine in its proper order, and to regulate its motion, which has been styled Reaction. This more nearly approaches to what may be regarded as a specific principle, and may, perhaps, be considered as a mode of self-adjustment, which operates in all cases upon the same substances, and by the intervention of the same functions. If the action of a vital part be by any cause diminished, provided the defect be within certain limits only, the diminution of action becomes the immediate cause of an increase of power in the part by which it is enabled to overcome the obstacle, and restore the balance of the system. This capacity of reaction appears to reside as well in the contractile as in the sensitive parts, and is one of the most efficient means which is employed by the Physician for restoring the functions to their state of healthy action, when this has, by any means, become deranged.(k) Secondly, One of the principal vital powers is, as we have seen, Motion, The power in parts already formed, and which have been divided into common, afof Motion fecting every part of membrane throughout the frame, and proper, which and Con- affects only particular organs for the purpose of peculiar and anomalous motions. The motions affecting the membranes of the whole frame are contractility or irritability. Some have supposed that mere contractility is characterized by a simple and not very perceptible effort of the membrane to contract upon its contents, especially upon its source of moisture, the serous vapour, and to propel this into the lymphatic system. Irritability (more properly muscular contractility) is a condition peculiar to the muscles, and it is marked by an oscillatory or tremulous motion distinguished from simple contraction, both by occurring far more easily on the application of any strong stimulus, and by being attended with a much more considerable contraction.() The contractility of membrane is the chief cause of strength, health, and beauty, since upon it depends the vital elasticity and fulness, and indeed the tone of parts, for, by its means, the membrane, to mention one, only, of its functions, absorbs during health, the serous fluid, like a sponge, and propels it into the lymphatic vessels. In disease, on the contrary, having lost its tone, it is filled with water, giving rise to oedema, or watery effusion. Hence, after death, even in young subjects, full of juices, the back, loins, and buttocks, having for some time lost their vital tone, are, if the body be horizontally placed on the back, depressed and flattened by the superincumbent weight, and therefore this appearance may be regarded in cases otherwise doubtful, as one of the indisputable signs of death.(m) The various internal motions, contractions, and elongations of the membrane also contribute, of themselves, to resist decomposition and putridity. (i) 3 Bost. 145, 146. (k) 3 Bost. 145, 146; see also Jackson, Prin. Med. 604, 605. (1) 2 Dunglison, 502 to 505. (m) El. Blum. 4 edit. 27 to 37, and see 1 Bell's Anat. chap. ix. of the Muscular Power, 378; Jackson, Prin. Med. 266. PROPER TIES, &c. But the precise cause or causes of muscular contraction appear as yet CHAP. II. unascertained, at least with any satisfactory degree of certainty. Dr. III. THE Bostock observes, that two distinct questions here present themselves: ESSENTIAL first, what is the efficient cause of the contraction of the fibre, or by what physical cause is it produced? and, secondly, what is the cause of contractility, or that property of the fibre which produces contraction? That learned physiologist remarks, that both these questions are highly inte- What is the resting, but that they unfortunately are both of them of very difficult so- cause of lution.(n) Many physiologists of the first eminence have, of late, endea- muscular voured to account for the cause of contractility, by insisting that it is at- lity. contracti Semble, tributable to the natural attraction of the fibres to each other; others call it the attraction of life, and others term it as an attraction depending upon electricity the operation of the vital principle. But Dr. Bostock shows that though by the conwe admit the truth that during life there exists such attraction, yet that tact of the it affords no explanation of the cause of contractility; and he concludes nerves and that, in the present state of our knowledge, contractility ought to be re- muscles. garded as the unknown cause of known effects, as a quality attached to a peculiar species of matter possessed of properties peculiar to itself, and which we are not able to refer to any general principle.(0) Of late we have seen that the contractility of the muscles has been ascribed by some to electricity, occasioned by the nerves coming in contact with the muscles, which causes contraction, and which again is controlled by the will, and there seems to be strong ground to expect that farther experiments may establish this position.(p) ness or ty. The third vital power is Sensation or Sensibility, or, more properly, Thirdly, Sensitiveness. This, it is laid down, is peculiar to the nervous medulla Sensation, communication from the sensorium. It bears the title of vis nervæ, and Sensitiveis the cause of perception in the mind when irritation (and, consequently, Sensibilicontractility) is excited in parts to which it is distributed.(q) Sir Everard Home has considered that the brain is composed of small globules connected together by a peculiar gelatinous substance, which he conceives constitute a very important part in the animal economy, and he even insists that there can be no doubt that the communication of sensation and volition more or less depends upon it, and he even regards it as the very essence of life.(r) Dr. Bostock observes, that, with respect to the relation which the different parts bear to each other, it has been generally supposed that the brain is the centre of the Nervous System, or is that part to which all the others are subservient, and that the Nerves receive impressions from external objects, and transmit these impressions to the Brain, where they become sensible to the Mind, constituting Perceptions; and that view of the subject is, in the main, correct, although the experiments and discoveries of the modern anatomists have led to some modification; but that all questions respecting the action of the Nervous System are involved in much obscurity, and which, in some measure, attaches to the nature of the subject.(s) The present doctrine is, that however essential sensation may be to the Perfection of Man, yet that the Nervous System is not necessary for the mere continuance of animal life, though it is indispensable as regards the functions of Organic Life, namely, respiration, círculation, digestion, &c.(t) (n) 1 Bost. 125. (0) 1 Bost. 132 to 135. (p) Prevost and Dumas's Hypothesis of Muscular Contraction, and see 3 Bost. 281; and see 1 Bost. 167, as to Electricity being the cause of contractility, ante, 42, note (r,) and post, as to the Muscles; see also Dr. Dunglison, Human Physiology, (9) El. Blum. 30; 1 Bost. 192. (t) 1 Bost. 268, note; 195, note. CHAP. II. Most of these modes of vital energy, though necessarily distinguished III. THE into orders, are intimately connected, the membrane forming the basis of ESSENTIAL SO many organs, and the seat of their contractibility is interwoven also PROPER with the irritable muscular fibres and the sensible nerves. TIES, &c. Vitality exists as well in the fluids as in the solids, or at least in the Blood, though the incorruptibility of the latter during life might be attriCombined butable to the perpetual changes which it undergoes, especially in respiraview of all tion.(u) Indeed, it has been truly observed by a most able commentator, and other that Harvey's doctrine of the life of the Blood is the best established doctrine of modern physiology.(x) these vital powers. As these changes during life necessarily imply that the fluid parts are constantly being converted into solid structures to maintain their growth and nutrition, and, again, that the particles which had for some time formed part of the solids, are taken up by the absorbent vessels and carried back into the current of the circulation, to make way for the new matter about to be deposited in their stead, it follows that the ultimate constituents of the solids and fluids are identical, else this ceaseless conversion of the one into the other could not take place, the only difference between them being as to their mode of composition or aggregation. (y) It seems, therefore, to be considered, that the vital power of resisting putrefaction is principally attributable to respiration, and the circulation of the blood and incessant motion of the parts, which prevent stagnation and inertness, which are the preliminaries to putrefaction; and, according to the experiments of Mr. Brodie, Dr. Philip, and the opinion of Soemmering, Dr. Bostock, and others, the nervous system is not necessary to the mere continuance of animal life, though without its due exercise, man would be a mere automaton.(z) It is, however, admitted by the ablest writers, that, beyond this truth, the essential nature of life is still an impenetrable mystery, and no more a subject for philosophical inquiry than the essential nature of Attraction or of its counteractor, Heat; but that life never originates, but began at the creation, and is communicated to assimilated matter, and propagated from parent to offspring.(a) According to Mr. Lawrence, organized differs from unorganized matter merely by the addition of certain properties which are called vital, as sensibility, (more properly sensitiveness,) and irritability, (more properly contractility.) Masses of matter, endowed with these properties, become organs, and systems of organs constitute an animal frame, and execute distinct sets of Purposes or Functions. Life is the assemblage of all the functions, and the general result of their exercise.(b) Some authors have therefore indulged in fanciful illustrations; thus, the human frame has been compared to a musical instrument, (as a barrel organ,) possessing systematic arrangement of parts played upon by peculiar powers, and executing particular pieces or purposes; life is the music produced by the general assemblage or result of the harmonious action. So long as either the vital or the mechanical instrument is duly wound up by a regular supply of food, or of the winch, so long the music will continue; but both are worn out by their own actions, and when the machine will no (u) El. Blum. 31, 61, 62; 2 Dunglison, Phy. 52, 507. (x) See note of Mr. C. Bell, 1 Bell's Anat. 511, in which he denies the doubt as to the vitality of the blood, in 1 Bell, 518, 519; see also 2 Good, 42. (y) 1 Bost. 101 to 105, every part of the body is probably removed in process of time, particle by particle, in a manner precisely the reverse of that in which it was formed, and this process can only be effected by the absorbent system. Ante, 42, 44. (z) 1 Bost. 268, note. (a) El. Blum. 4th edit. 64, 65, and 510; 1 Bost. 192, 194. (b) Lawrence, Introduction to Comparative Anatomy and Physiology, 120. |