When the waste of the tissues is more rapid than their replacement by nutrition, atrophy is said to take place; and this may affect either the whole body, or individual parts. General atrophy, mamsmus, or emaciation, may result from an insufficient supply of plastic matter, from want of formative power in the tissues themselves, or from their too rapid disintegra tion. The insufficiency of the supply of nutri tive matter may depend either on deficiency in the azotized substances ingested as food, or on imperfect performance of those processes by which they are convened into the plastic element,—fibrin. Bence, even when there is an ample supply of food, atrophy. may talce place to a very severe extent, in consequence of disordered digestion, or of want of vital power in the fibrin-elaborating cells. Ag,ain, we have reason to believe that the formative power in the tissues themselves may be diminished, so as to check the process of nutrition, even when the pla.stic material is supplied ; thus there seems to be a complete stoppage of this action in fever, and a diminution of it in that irritable state of the system, which results from excessive and prolonged bodily exertion or anxiety of mind, especially when accompanied by want of sleep. It is difficult to separate this cause, however, from mal-assimilation on the one hand, or too rapid decay of the tissues 011 the other : for we know that, in such states, there is a tendency to imperfect elaboration of the fibrinous element, and at the same time an unusually rapid dIsintegration, as mani fested by the increased amount of urea in the urine. The influence of excessive waste in causing atrophy of the body is well shown in the cases of diabetes mellitus and colliquative diarrhcea ; for in both these, the increase and depravation of die secretions are undoubtedly to be regarded as the effects, and not the causes, of the textuml changes with which they are as sociated. Colliquative diarrhcea is a constant occurrence on the last day or two of life in animals reduced by starvation, and is accom panied by that fcetid odour of the body, which indicates that decomposition is already going on throughout the system. The same thing occurs as the ordinary termination to many diseases of exhaustion ; in which inanition is unquestionably the immediate cause of death. Partial atrophy may occur in consequence of disuse of the organ affected, occasioning inactivity in its formative processes; or as a result of a deficiency of nu triment, occasioned by an obstruction to the circulation. Of the operation of the former cause we have many examples in the ordinary processes of the economy. Thus the uterus is atrophied, relatively to its previous condition, I as soon as parturition has taken place ; and t mammary glands, when lactation has been continued. It is probably in part to this ca and in part to the diversion of the blood i other channels, that we are to attribute atrophy of many parts, as the developement the system advances, which at an earlier per' were of large comparative size,—such as corpora Wolffiana, the supnirenal capsules, the thymus gland. Many instances might adverted to, of the influence of suspension functional activity, as a result of disease injury, in producing local atrophy. One of the most common cases is the atrophy of rnuscles which is consequent upon their disuse. This disuse will produce the same effect, whether it be occasioned by paralysis, which prevents th nervous centres from exciting the muscles cohtraction ; or by anchylosis, which in poses a mechanical impediment to their or by fmctures or other accidents, the paration of which requires the limb to be k at rest. Or even if, without having s frorn any injury, a limb be fixed duri time in one posture, its rnuscles w come atrophied, as is seen in the case of Indian fakirs. It has been shown by Dr Reid, that the atrophy of the muscles, and t consequent loss of contractility, is not to be i puled to the withdrawal of nervous influence) in any other way than as producing cessation of their activity ; for he found that, when the rims cles of one leg of a frog, both whose crural nerves had been divided, were daily exercised by gat vanism, they retained much more of their usey size and firmness than those °film leg which 411,0 left at rest. It case has fallen under the writer's observation, in which both limbs were affected with almost complete (hysteric) pamplegia ; but one was also frequently seized with violent cramps, from which the other was free ; the difference in the muscularity of the two Iiinbs WaS very striking, and was evinced by the greater circumference of the one affected with crarnps (which was an inch and a half larger round than the other), as well as by its greater firmness of flesh. Similar facts may be ad duced, in regard to atrophy of nerves, from interruption oF their normal function. Thus when the cornea has been rendered so opaque by accident or disease, that no light can pene trate to the interior of the eye, the retina and the optic nerve loSe, after a time, their charac teristic structure ; so that scarcely a trace of the peculiar globules of the former, or of the nerve tubes of the latter, can be found in them. 'These and similar facts are readily understood, when connected by the general principle for naerly laid down,—that every proper vital operation involves an act of nutrition ; in such a manner that, whilst the vital properties ofany part are dependent upon its due nutrition, the amount of its nutrition will in return depend upon the degree in which these properties are exercised.
Partial atrophy may depend, however, upon causes of a purely mechanical nature ; such, for example, as produce an interruption of the current of blood through the part. This may result from changes in the arteries supplying it, such as ossification, or other forms of obstruc tion. Or it may be consequent upon disease in the part itself; as when the deposits produced by inflammation tend to contract, and thus to press upon the vascular structure, which fre quently happens in the lungs, liver, and kidneys; or when the inflammation occurs in the vessels themselves, causing adhesion of their walls, and obliteration of their tubes ; or when a new growth absorbs into itself all the nutritive materials which the blood supplies.
Abnormal forms of the nutritive process.— Under the preceding head we have considered the chief variations in the deg,ree of activity that are witnessed in the ordinary or normal conditions of the nutritive process —that is, those conditions in which the prOducts are adapted by their similarity of character to re place those which have been removed by dis integration. But we have now to consider those forms of this process, in which the pro ducts are ahnormal,—being different from the tissues they ought to replace. We shall con fine ourselves to a brief examination of the two most important of these states ;—that which is termed Inflammation, and that which gives rise to tubercUlar deposit. The former results from an excess of the plastic element in the blood : the latter from a depraved condition of it, whemby its plasticity is impaired or de stroyed.
Notwithstanding all the attention which has been given to the state of the vessels in inflam mation a careful considemtion of its phenomena, with the light which recent investigations have thrown upon these, leads us to attach com paratively little importance ter this, and to seek for the essential character of' the_process else where. The researches of Addison, Williams, Barry, Gulliver, Andral, and others, all seem to point to the following conclusions.-1. That there is a peculiar efflux or determination of the white corpuscles of the blood towards the in flamed part. 2. That the total amount of these corpuscles in the circulating blood undergoes a great increase. 3. That the quantity of fibrin in the blood augments in proportion to the ex tent and intensity oF the inflammation ; and this even when it was previously, from the influence of some other morbid condition, below the usual standard. With its quantity, its plasticity or tendency to organization also increases in a, healthy subject. Now when these facts are compared together, and are con nected with those formerly adduced, in regard to the probable function of the white corpuscles of the blood, they lead almost irresistibly to the conclusion, that the process of inflammation essentially Consists in an undue stagnation of the white corpuscles of the blood in the vessels of the part, an excessive multiplication of these by the ordinary process of generation, and a con sequent over-production of fibrin. By these changes, and by the results which follow them, inflammation may be distinguished from the various forms of hyperwmia and congestion. To the results, then, we shall next direct our attention.
It may be inferred, we think; from various phenomena, that whilst the formative power of the blood is increased in inflammation, that of the tissues is diminished. Certainly this is the case in regard to the system at large, when febrile irritation has been established ; for, not withstand ingthe increased plasticity of the blood , we see the body wasting,, instead of increasing in vigour, And it may be inferred, also, in regard to the tissues of the part affected, from the tem: dency to atrophy and disintegration which they exhibit ; and which is greater (leading even to the death of whole parts) in proportion as the in flammation is more intense, and as the tendency to the deposit of new products is the innore decided. That a stagnation of blood takes place in the vessels of the inflamed part is another general fact, which throws some light upon the nature of the process ; for this stag nation is obviously favourable to the transu dation of the fluid plasma of the blood, through the walls of the vessels, into the surrounding tissue, or upon a neighbouring surface. This deposition of the fibrinous element, possessing a high degree of plasticity, and capable of spon taneously passing into simple forms of tissue (which may be gradually replaced by higher forms, when penetrated by vessels from the surrounding parts), may be regarded as the first characteristic result of inflammation. That this deposition of the fibrin, which has accu mulated to an unusual extent in the blood, should take place only in the inflamed part, cannot perhaps be very readily accounted for; but we see that, when the inflammatory diathesis is once established,—or, in othez words, when the quantity of fibrin in the cir culating part is much increased,—local inflam mat.ons will be excited by very trifling causes (at other times quite inoperative), which are followed by the same results as the original one.