PERMANENT TISSUES.
isolated cells, for example, passing over into those with blended walls ; and again, a tissue which usually consists of isolated cells, occasionally exhibits in different situations coalesced cells. Such difficulties, however, present themselves in all classifications of natural objects. Nature is very unwilling to accommodate herself to our schemes. The object of her aim is quite opposed to that of our intellect. She accords and accommodates all contrarieties by gentle transitions: the intellect disjoins, and seeks everywhere for strongly-marked contrasts. If, however, regard be had to the most important structure only in each individual tissue,—for example, in the nervous system, to the nervous fibres and not to the ganglion-globules, in cellular tissue, to its fibres and not to the fat, and so forth,—and further, if we regard only that which is the general rule as to these structures, all tissues may then be readily brought under these five classes. With the desire of making this work as complete as possible, I have applied this arrangement to all the tissues in the way which has appeared to be most probably correct, according to the investigations I have hitherto made. Those researches are, however, far from complete, and continued observations may perhaps render it necessary, at some future time, to assign a different position to some of the tissues. This may serve as a preliminary sketch:
Class I. Isolated, independent cells. To this class the cells in fluids pre-eminently belong; Lymph-globules, Blood-corpuscles, Mucus- and Pus-corpuscles, &c.
Class II. Independent cells united into continuous tissues. Such as the Horny tissues and the Crystalline lens.
Class III. Cells, in which only the cell-walls have coalesced: Cartilage, Bone, and the substantia propria (ivory) of the Teeth.
Class IV. Fibre-cells: Cellular (areolar), Fibrous, and Elastic tissue.
Class V. Cells, im which both the cell-walls and cell-cavities have coalesced: Muscle, Nerve, Capillary vessels.
