Structure and a portion of cellular tissue void of adipose substance be ex amined with the naked eye, and for this purpose that which intervenes between very recent muscu lar fibres may be advantageously selected, it will be seen that it is composed of an immense num ber of delicate and semi-transparent filaments, having very much the appearance of the finest threads of a spider's web. These fibrils cross each other in various directions, and in this manner intercept innumerable spaces, which communicate one with another, and exhibit a vast variety of figures. The small spaces or areolT which are thus produced constitute what are called the cells of this tissue ; but as there is nothing determinate either in their size or shape, which evidently vary according to the degree of traction exercised in separating the filaments ; as they communicate together, and consequently are not circumscribed ; as they are in fact simply the interstices left between the fibres, the expression in common use is calculated to convey an erroneous idea of the real nature of these spaces.
If the investigation be prosecuted with the aid of a powerful microscope, a very beautiful appearance will be presented, of which it is impossible to convey an adequate idea by any description. We shall still observe fibres cross ing in all directions ; but although I have had many favourable opportunities of making these observations, I have never been able to detect in the cellular fibre that linear arrangement qf globules described by Dr. Milne Edwards, and which has of late years been very generally supposed to pervade all the elementary fibres of the body. A number of globular particles may, it is true, be seen at irregular distances, either clustered together or dispersed in an isolated manner, but they do not enter into the forma tion of the fibre. The results, then, of careful inspection disprove the ideas of former anato mists, some of whom, Ruysch and Mascagni for example, supposed that the cellular fibre was entirely vascular, whilst others imagined it to be an expansion of the nerves : it is now generally admitted that the basis of the cel lular substance is a solid and elementary fibre ; and although to the naked eye it often presents a membranous form, yet microscopical observa tion evinces that the plates of membrane are distinctly composed of solid fibres. The in terstices or cells always contain in health a very thin albuminous fluid, which has a great resemblance to the secretion of the serous mem branes, and also to the serum of the blood ; and hence it is often termed the cellular serosity. This fluid, which must be regarded as an in tegrant part of this tissue, has a great influence on its properties, so that if it be entirely re moved, as by desiccation, the membrane be comes hard and brittle, and its elasticity is almost lost ; or if it be accumulated in excess, as we often see it in disease, the elastic force is also destroyed.
Bloodvessels and lymphatics.—An inquiry into the relations which exist between the cel lular and vascular tissues, would lead to the important question, how far vascularity is essen tial to organization ? Without entering into this investiaation, it may be remarked that the cellular substance is provided with blood vessels; and although the greater number of these merely traverse the membrane in order to reach other parts, yet the phenomena of nutri tion and absorption sbew that a vascular appa ratus must exist in connexion with the cellular tissue.
Nerves.—It is impossible to trace any ner vous filaments to the cellular fibres, although such threads may be seen passing between them to the neighbouring organs. The insensibility in its healthy state also seems to indicate the absence of nerves; but as pain is experienced during inflammation, we must admit the ex istence of some communication with the senso rium.
Chemical composition. —The cellular sub stance contains, like all the soft solids of tlie body, a large quantity of water : when this is evaporated, the fibres and cells adhere to each other, and present a membranous appearance. Analysis shews that albumen and gelatine com pose this substance ; the former predominating, and being in a state of coagulation, bestows on it the necessary degree of firmness and re sistance.
Properties.—As we shall have occasion in a future article (see MEMBRANE) to consider this subject more minutely, it will suffice if we here remark that the most important property of the cellular substance is a species of contrac tion which produces in all the soft parts a con stant state of tension or tone, which is one of the most remarkable qualities of living bodies. The cause of this peculiar condition, in what ever part it is evinced,—in the skin, in the cellular tissue, in the muscles, in the vessels, &c.—is the result of a property inherent in mem branous matter, which some authorities refer to muscular contractility, and others to elasticity ; whilst many eminent physiologists, denying both these hypotheses, conceive that the con traction to which we are alluding is of a character sui generis, and which they have called tonicity, vis cellulosa, tonic contraction, contractility of tissue,&c. I confess that none of these theories have ever been to me satisfactory; because, as regards the first, there is no resem blance between the phenomena connected with the contraction of membranous parts, and those of muscular contraction ; whilst, as respects the second, the resiliency by which the skin re covers itself after pressure has been made on the external surface, and the retraction and separation of the sides of an incision inflicted on the integument, being observed only during life, and never after death, prove that the results of cellular contraction are, in some important respects, different from those of common elas ticity. Those writers who, in consequence of the difficulty of referring the phenomena under consideration to either of the known causes of contraction, viz., muscular contractility and elasticity, have imagined the existence of a new kind of contractile power, have, without ad ducing any sufficient proof in corroboration of their views, bad recourse to an expedient but too frequently adopted by physiologists when the real nature of any vital process escapes their detection.