352 THE MICROSCOPE. 



tlie nucleus is outside, the fibres of the cell and those of the nucleus 

 unite, fibre by the side of fibre. As an example, we have the bone of 

 the tooth ; in this the fibres of the cell and nucleus alternate. Again, 

 if the nucleus be arranged externally, it unites across either behind or 

 in front, and thus a spiral filament is formed : this is seen in cellular 

 tissue and tendon. The last-described form may alternate with that 

 described before it, and there are all intermediate shades of difference. 

 Nuclei sometimes disappear when they are very nearly developed, as in 

 the cornea of the eye. 



Action of Cells. The subsequent changes of these depend in a 

 great degree on endosmosis. The nature of the membrane is a neces- 

 sary condition, for it determines the way in which the stream should 

 pass ; and we find in general that the current is from the rarer to the 

 denser fluid. If we take common salt and fill a tube with it, and put the 

 latter in water, we find that the salt rises, from the water having passed 

 into the tube, and at the same time the water outside is saltish to the 

 taste. It is not a constant circumstance that the stream is from the 

 rarer to the denser fluid ; with alcohol and water, for instance, the 

 stream is from the latter to the former. Mineral substances permit of 

 endosmosis, as pipeclay and chalk, in a low degree ; but sandstone does 

 not allow of endosmosis at all ; thus proving that there must be some- 

 thing in the nature of the material to be permeated. 



As to the processes of secretion, these depend in a great degree on 

 endosmosis, inasmuch as the materials are drawn from the blood, and 

 so thrown off. 



Intercellular Substance. In certain tissues the basis is made up of 

 a homogeneous matter, granular or fibrous, or of a tissue composed of 

 cells. The intercellular tissue must be the cytoblastema after the cells 

 have been formed from it, and differs in quantity in different tissues ; 

 in some it is very slight in quantity, so that it has been overlooked ; 

 but still the parts are held together, and this must be by cytoblastema, 

 which is proved by chemical action. In epithelium and other parts, on 

 the contrary, it is in great quantity. This intercellular substance is 

 sometimes formed into fibre, whether it be constituted of cytoblastema 

 or of cells, and may exist in three conditions : 1st, as a homogeneous 

 substance ; 2d, as granular matter ; 3d, as fibre. As an example of 

 the first kind we have the epidermis, and of the second the cellular 

 tissue. As hyaline membrane it exists in cartilage. In some carti- 

 lages it is by age developed into fibre, called cartilage fibre an ex- 

 ample is that between the vertebra ; for the part in immediate connec- 

 tion with the bone, Wharton Jones has shown to be true cartilage. 



