xxvi NUTRITION OF THE TEXTURES. 



residuary blastema remains as intercellular substance, or whether a part is 

 again absorbed into the vessels, is not known. In other non- vascular 

 tissues, such as articular cartilage, the nutrient fluid is doubtless, in like 

 manner, conveyed by imbibition through their mass, where it is then 

 attracted and assimilated. The mode of nutrition of these and other non- 

 vascular masses of tissue maybe compared, indeed, to that which takes 

 place throughout the entire organism in cellular plants, as well as in polypes 

 and some other simple kinds of animals, in which no vessels have been 

 detected. But even in the vascular tissues the case is not absolutely 

 different ; in these, it is true, the vessels traverse the tissue, but they do 

 not penetrate into its structural elements. ThuS the capillary vessels of 

 muscle pass between and around its fibres, but do not penetrate their 

 inclosing sheaths ; still less do they penetrate the fibrillse within the fibre ; 

 these, indeed, are much smaller than the finest vessel. The nutrient fluid, 

 on exuding from the vessels, has here, therefore, as well as in the non- 

 vascular tissues, to permeate the adjoining mass by transudation, in order to 

 reach these elements, and yield new substance at every point where renova- 

 tion is going on. The vessels of a tissue have, indeed, been not unaptly 

 compared to the artificial channels of irrigation which distribute water over 

 a field ; just as the water penetrates and pervades the soil which lies be- 

 tween the intersecting streamlets, and thus reaches the growing plants, so 

 the nutritious fluid, escaping through the coats of the blood-vessels, must 

 permeate the intermediate mass of tissue which lies in the meshes of even 

 the finest vascular network. The quantity of fluid supplied, and the dis- 

 tance it has to penetrate beyond the vessels, will vary according to the 

 proportion which the latter bear to the mass requiring to be nourished. 



We have seen that in the cuticle the decayed parts are thrown off at the 

 free surface ; in the vascular tissiies, on the other hand, the old or effete 

 matter must be first reduced to a liquid state, then find its way into the 

 blood-vessels, or lymphatics, along with the residual part of the nutritive 

 plasma, and be by them carried off. But, in certain cases, the mode of 

 removal of the old matter is not clear ; as, for example, in the crystalline 

 lens, which is destitute of vessels, and grows by deposition of blastema and 

 formation of cells at its surface ; here we should infer that the oldest parts 

 were nearest the centre, and if we suppose them to be changed in nutrition, 

 it is puzzling to account for their removal. 



From what has been said, it is clear that the vessels are not proved to perform any 

 other part, in the series of changes above described, beyond that of conveying matter 

 to and from the scene of nutrition ; and that this, though a necessary condition, is 

 not the essential part of the process. The several acts of assuming and assimilating 

 new matter, of conferring on it organic structure and form, and of disorganising 

 again that which is to be removed, which are so many manifestations of the metabolic 

 and plastic properties already spoken of, are performed beyond the blood-vessels. It 

 is plain, also, that a tissue, though devoid of vessels, and the elements of a vascular 

 tissue, though placed at an appreciable distance from the vessels, may still be organised 

 and living structures, and within the dominion of the nutritive process. How far the 

 sphere of nutrition may, in certain cases, be limited, is a question that still needs 

 further investigation ; in the cuticle, for example, and its appendages, the nails and 

 hairs, which are placed on the surface of the body, we must suppose that the old and 

 dry part, which is about to be thrown off or worn away, has passed out of the limits 

 of nutritive influence ; but to what distance beyond the vascular surface of the skin 

 the province of nutrition extends, has not been determined. 



Regeneration. When part of a texture has been lost or removed, the 



