There are many organs, in which the cellular texture is hardly apparent, because their structure is so compact; some authors have even denied the existence of it in them. But in many of these organs, maceration, by filling in an insensible manner the fibres with water, parts them by degrees, and makes apparent the cellular texture which separates them, as we see especially in the tendons, in the fibrous membranes, &c. Ebullition, which takes from some their nutritive substance, for example gelatine, leaves a membranous residue which is evidently cellular. In all, even the bones and cartilages, the production of fleshy points, or granulations, which, as we shall see, are essentially of a cellular nature, proves the existence of this internal texture, of which they are only the elongations. The same may be said of the bones becoming soft, and fleshy, and of fungous tumours of the other systems, diseases in which this texture becomes very apparent, because the organ loses by them its compact structure, and takes one that is more loose and spongy, and which exposes that which is placed in the interstices of the fibres.
ARTICLE SECOND.
OF THE CELLULAR SYSTEM, CONSIDERED INDEPENDENTLY OF THE ORGANS.
After having considered the cellular system in relation to the organs, let us consider it separate from all the parts that it covers and penetrates, in order to represent it as a body continued on all sides, found every where in the interstices of the organs and being analogous in this point of view to almost all the other primitive systems. Let us trace it in the head, the trunk, and extremities.
I. Of the cellular system of the head.
The cranium and face differ extremely as it respects the cellular texture; it is found in very small quantity in the first, and in great abundance in the second.
Cellular texture of the cranium.
The interior of the cranium has but very little cellular texture; it is even apparently destitute of it. If, however, we raise the tunica arachnoides, where the vessels enter and where the nerves go out, we shall find a small quantity, which is remarkable for its delicacy and transparency. The pia mater is principally formed by this texture, and the texture of this membrane appears to be continued with that of the brain; this, however, is extremely hard to be demonstrated; it is not proved by maceration, and it is scarcely seen except in fungous tumours.
The communications of the cellular texture of the interior of the cranium are very numerous.
1st. In front it enters the orbit by the optic foramen and the sphenoidal fissure; hence the redness and heat of the eye in paraphrenitis,[5] the influence of which is propagated by these communications, as well as by the continuity of membranes. It enters the nostrils by the foramina in the cribriform plate; to this perhaps we may attribute the weight, and pain of the head in coryza.