Page:Cellular pathology as based upon physiological and pathological histology.djvu/62

56 LECTURE II cells have attained specific, higher forms of development, by means of which their constitution has acquired a type entirely peculiar; indeed, in part so peculiar, as to appertain exclusively to the animal economy. These are the tissues which are really characteristic of animals, although a few among them exhibit transitions of vegetable forms. To this class belong the nervous and muscular systems, the vessels and the blood. Herewith is the list of tissues concluded.

You must now proceed to consider, in what respect, in this summary of the result of histological researches, a contrast is afforded to what was formerly, chiefly in imitation of Bichat, regarded as constituting a tissue. Bichat's tissues would, for the most part, not so much represent what we now regard as the subjects of General Histology, as what we must rather designate as belonging to Special Histology. For, if we regard the tissues in the light they were formerly regarded; if we, for example, separate tendons, bones, and facise, from one another, we then obtain an extraordinary variety of categories (Bichat had twenty-one), but there are not quite as many simple forms of tissue to correspond to them.

In accordance with modern notions, the whole domain of anatomy should first be divided into the categories of General Histology (tissues properly so called). Special Histology, then, takes up the instances, in which a combination of tissues, sometimes very different, into a single whole (organ) takes place. Thus we speak, for example, of osseous tissue; but this tissue, the tela ossea of general histology, does not of itself form bone, for no bone consists entirely of tela ossea, but it has necessarily superadded at least periosteum and vessels. Nay, and from this simple conception of a bone, every bone of considerable size, for example, a long bone