GLANDS.

CONNECTIVE TISSUE.

41

tions of cells, which usually form open canals. With the exception of the glands whose functions are uncertain, such as the thyroid body and supra-renal capsules, there are in the human body only the ovaries which form an exception to this rule, inasmuch as their follicles are only open at times yet they too must be open when the specific secretion of ova has to take place. In most glands there is found indeed besides a certain quantity of transuded fluid, but this only constitutes the vehicle which floats off either the cells themselves, or their specific products. Suppose, for example, that in one of the ducts of the testicle a cell, in which there is a production of spermatozoa becomes detached, then there transudes at the same time a certain quantity of fluid, which carries them away; but what makes the semen, semen, and constitutes the specific character of the action is the peculiar power of the cell; the mere transudation from vessels is no doubt a means of conveyance onwards, but does not constitute the specific action of the gland nor the real secretion. In an analogous manner, in all the glands of which we can follow the action in all its details with precision, the essential peculiarities of their energy are derived from the development and transformation of epithelial cells.

The second histological group is formed by the connective tissues (Gewebe der Bindesubstanz). This is the subject in which I take the most interest, because it was here that my own observations, which have led to the result to which I directed your attention at the beginning of these lectures, originated. The alterations which I have succeeded in introducing in the views of histologists with regard to the whole group have, at the same time, enabled me to give a certain degree of roundness and completeness to the cellular theory.

Previously, connective tissue had nearly universally been regarded as essentially composed of fibres. On examining

loose connective tissue in different regions, as, for example, beneath the corium, in the pia mater, subserous and submucous cellular tissue, we find wavy bundles of fibres, the socalled wavy connective tissue (Fig. 19, 4). This wavy character, which is interrupted at certain intervals, so as to give rise to a kind of fasciculation, could, it was thought, with the less hesitation be attributed to the presence of separate fibres, because at the end of each bundle isolated filaments could in reality be seen to protrude. In spite of this, however, an attack was made upon this very hypothesis, somewhat more than ten years ago, and has proved of very great

importance, though in a manner different to that which was intended. Reichert endeavoured, namely, to show that the fibres were only an optical illusion produced by folds, and that connective tissue in all parts formed a homo

Fig. 19. A. Bundle of common, wavy, connective tissue (intercellular substance), splitting at its end into fine fibrils.

B. Diagram of the development of connective tissue, according to Schwann. a. Spindle-shaped cell (caudate corpuscle, fibro-plastic corpuscle of Lebert), with nucleus and nucleolus. b. Cleavage of the body of the cell into fibrils.

C. Diagram of the development of connective tissue, according to Henle. a. Hyaline matrix (blastema), with nucleolated nuclei regularly distributed through it. b. Fibrillation of the blastema (direct formation of fibrils), and transformation of the nuclei into nucleus-fibres.

THEORIES RESPECTING CONNECTIVE TISSUE.

43

geneous mass, endowed with a great tendency to the formation of folds.

Schwann had, in reference to the formation of connective tissue, assumed that there originally existed spindle-shaped cells, the caudate corpuscles (geschwänzte Körperchen) (fibro-plastic corpuscles of Lebert), which afterwards became so famous; and that out of these cells fasciculi of connective tissue were directly developed by the splitting up of the body of the cell into distinct fibrils, whilst the nucleus remained as such (Fig. 19, B). Henle, on the other hand, thought the only conclusion his observations would warrant was, that there were originally no cells at all, but that nuclei only were formed in the blastema at certain intervals; whilst the fibres, which afterwards appeared, were produced by a direct fibrillation of the blastema; and that, whilst the intermediate substance was thus being differentiated into fibres, the nuclei gradually became elongated, so as at length to run into one another, and thus give rise to peculiar longitudinal fibres, nucleus-fibres (Kernfasern) (Fig. 19, C). Reichert took an extremely important step in opposition to these views. He showed, namely, that originally there were only cells, and those in great abundance, between which intercellular substance was deposited. But the membrane of the cells became, he thought, at a certain period, blended with the intercellular tissue, and then a stage was reached analogous to that described by Henle, in which there no longer existed any boundary between the original cells and the intermediate substance. And, finally, he imagined that the nuclei, too, entirely disappeared in some instances, whilst they were preserved in others. On the other hand, he positively denied the occurrence of the spindle-shaped cells of Schwann, and declared all such, as well as the caudate and jagged cells, to be just as much artificial products as the fibres, which were said to be seen in the interven

ing substance, were a false interpretation of an optical image.

Now, my own investigations have shown, that both Schwann's and Reichert's observations, up, to a certain point, have some foundation in truth. That, in the first place, in opposition to Reichert, spindle-shaped and stellate cells indisputably do exist (Fig. 20); and secondly, in opposition to Schwann, and with Reichert, that a direct splitting up of the cells into fibres does not take place, but that,

on the contrary, what is afterwards presented to our sight as connective tissue has really taken the place of the previously homogeneous intercellular substance. I have found, moreover, that Reichert, Henle, and Schwann, were wrong in maintaining that ultimately at best only nuclei or nucleusfibres remained; and that, on the contrary, in most cases the cells themselves preserve their integrity. The connec

Fig. 20. Connective tissue from the embryo of a pig, after long-continued boiling. Large spindle-shaped cells (connective-tissue corpuscles (Bindegewebskörperchen)), some isolated, some still imbedded in the basis-substance, and anastomosing one with the other. Large nuclei, with their membrane detached; cell-contents in some cases shrunken. 350 diameters.

FORMATION OF CONNECTIVE TISSUE.

4.5

tive tissue of a later period is therefore not distinguished in its general structure and disposition in any respect from that of an earlier date. There is not an embryonic connective tissue with spindle-shaped cells and a perfectly developed one without them, but the cells remain the same, although they are often not easy to see.

Essentially, therefore, this whole series of lower tissues may be reduced to one simple plan. Usually, the greater part of the tissue is composed of intercellular substance, in

which, at certain intervals, cells lie imbedded, which in their turn present the most manifold forms. But these tissues cannot be distinguished by one's containing only round, another's, on the contrary, only caudate or stellate, cells, but in all connective tissues round, long and angular cells may occur. The simplest case is where round cells lie at certain intervals, and intercellular substance

Fig. 21. Diagram of the development of connective-tissue, according to my investigations. 4. Earliest stage. Hyaline basis (intercellular) substance, with largish cells (connective-tissue corpuscles); the latter drawn up in rows at regular intervals; at first separated, spindle-shaped, and simple; at a later period anastomosing and branched. B. More advanced stage; at a, the basissubstance which has become striated (fibrillated), presents a fasciculated appearance on account of the cells imbedded in it in rows, the cells becoming narrower and smaller; at b, the striation of the basis-substance has disappeared under the influence of acetic acid, and the fine and long anastomosing fibre-cells (connective-tissue corpuscles), still retaining their nuclei, are seen.