NUTEITION OF THE TEXTURES. 15 



frequently the case with the corpuscles of connective tissue, and as is 

 seen in the process of development of blood-vessels and nerves. 



Intercellular substance. — Of the matter which lies between cells 

 — the intercelhilar substance — and its relation to them, it may be 

 observed that sometimes it is in very small quantity, and seems merely 

 to cement the cells together, as in epithelium ; at other times it is 

 more abundant, and forms a sort of matrix, or ground substance, in 

 which the cells are embedded, as in cartilage. It is homogeneous, 

 translucent, and firm in most cartilages, and pervaded by fibres in 

 yellow cartilage. In connective tissue it consists of fibres, with soft 

 interstitial matter, which is scanty in the denser varieties, but abundant 

 in the lax tissue of the umbilical cord ; in bone the intercellular sub- 

 stance is calcified and mostly fibrous. As to the production of the 

 intercellular substance, there can be little doubt that in cartilage it is 

 derived from the cells. Formed as capsules round the cells by excre- 

 tion fi'om their surface, or by conversion of their proper sulistance, and 

 being blended into a uniform mass, it accumulates while the cells 

 multiply, and while fresh material is supplied to them from the blood, 

 which they convert into chondrinous substance. The source of tlie 

 intercellular substance is not, in every instance, so apparent, but it 

 may be presumed that the cells have some influence in its nutrition 

 and maintenance. 



From what has been said it will be obvious that cells play an important 

 part in the ^'owth of textui'es. and probablj- in nutrition. The former jiro- 

 cess is usually accompanied by a great multiplication of cells, the peculiar 

 constituent of which — the protoplasm — seems to be specially endowed with the 

 faculty of f)ropagation by division, and of increase by apjiropriating and con- 

 verting new matter. It is conceivable that in this way it may serve for the 

 extension of growing tissue and the development of structiu'al elements from the 

 crude materials of growth. Again, in the nutrition of a mass of tissue the cnide 

 material may undergo preparation by the cells that lie in the interstices of the 

 structure. 



The existence of this protoplasmic germinative substance is very general, 

 perhaps indeed universal, in the animal and vegetable kingdoms. But whilst in 

 the great majority of organic beings it assumes the form of a nucleated cell 

 (protoplast, or monoplast), as the first condition of their organised structure, in 

 simpler modes of life and organisation it is not subject to the same limitation of 

 fonn and mass. In the m[/ccfo:oa {/ni/.i'ODii/ccfc.f), a ciu'ious tribe, heretofore 

 mostly reckoned among the fungi, but standing as it were on the debateable 

 ground between the animal and vegetable kingdoms, the protoplasm is extended 

 into reticular masses, or irregularly anastomosing trains {i>Iaf<inodia), spread over 

 the siu-face of Ijark and other bodies to which it parasitically clings ; whilst in 

 viV)rios and some other infusorial animalcules of the simplest kind, it ajjpears as 

 fine molecular 2>articles : but it is most jarobably derived from parents in aU 

 instances, however minute and apparently insignificant these may be, 



Tlie intercellular or ground substance, possesses in a high degi"ee the property 

 of combining with and reducing the salts of silver ■\\'hen jireviously impregnated 

 with them and exposed to the light. This method of staining, which was intro- 

 duced by His and von Recklinghausen, has furnished us with a ready means of 

 determining the position and form of delicate cellular elements in a tissue, since 

 these, remaining unstained by the reagent, stand out white upon tlie dark 

 ground : or in the case of an epithelioid tissue, appear as white polygonal areas 

 bounded by fine dark lines (compare figs, 108 and lOiJ, pp IGG, 1G7). 



