as very minute orifices upon the wall of the canal. Now since the different bone-corpuscles are in their turn distinctly connected with one another, means are afforded by which a certain quantity of juice taken up from the surface of the vascular canal is not diffused throughout the whole mass of tissue, but confined to these delicate, continuous, and specially provided channels, and forced to move onwards in canals which are inaccessible to injections from the vessel. For a time it was believed that the canaliculi could be injected from the vessel, but this is only possible when the vascular canal has become empty by maceration.

This is a condition precisely similar to what we observe in the teeth, in which the canaliculi can be injected from the pulp-cavity when empty. If a solution of carmine be injected into this cavity, the dental canaliculi are displayed in the form of numerous tubules running up to the surface side by side in a radiated manner. The substance of the teeth also forms a tolerably broad layer of non-vascular material. Vessels are found nowhere but in the pulpcavity, in proceeding from which outwards we find nothing but the proper substance of the tooth (dentine) with its system of tubes, which extend nearly up to the surface, and in the root of the tooth are directly continuous with a layer of real bony substance (cement) the corpuscles of which are seated upon the ends of the tubes. A provision for the conveyance of the juices similar to that which in bone originates in the marrow, here takes its rise in the pulp, whence the nutritive fluid can be conveyed up to the surface by the means of tubes.

These systems of tubes which are found in such a very marked form in bone and the teeth, are to be seen with far less distinctness in the soft structures, and it is chiefly for this reason, I imagine, that the analogy which exists between the soft connective tissues and the hard texture of bone has not been clearly comprehended. These systems are

CANALS IN THE SEMI-LUNAR CARTILAGES.

87

most distinctly seen in parts which are more of a cartilaginous nature, as, for example, in fibro-cartilage. But it is a fact of great significance that we find a series of transitional forms between cartilage and the other connective tissues, in which the same conditions are constantly repeated. In the first place, parts which chemically belong to the class of cartilages, for example, the cornea, which yields chondrine when boiled, although nobody regards it as real cartilage. But more striking is the arrangement in those parts in which the external appearance speaks in favour of a cartilaginous nature, but the chemical properties do not correspond, as for example in the semi-lunar cartilages (Bandscheiben) of the knee-joint, which are interposed between the femur

and tibia for the purpose of protecting the articular cartilage from too violent contact. These parts, which even now are generally described as cartilage, yield no chondrine on boiling, but gelatine; and yet in this hard connective tissue, we meet with the same system of anastomosing corpuscles that prevails in the cornea and in fibrocartilage, and it is displayed with unusual distinctness and

FIG. 36.

clearness. Vessels are almost entirely wanting in these cartilages, but in exchange they contain a system of tubes of rare beauty. On making a section, we see that the

Fig. 36. Section from the semi-lunar cartilage of the knee-joint of a child. a. Bands of fibres, with spindle-shaped, parallel and anastomosing cells (seen in longitudinal section). b. Cells, forming a network, with broad, branching, and anastomosing canaliculi (seen in transverse section). Treated with acetic acid. 350 diameters.

whole is in the first place mapped out into large divisions, exactly like a tendon; these are subdivided into smaller ones, and these are pervaded by a fine, stellate system of tubes, or, if you will, of cells, inasmuch as the notion of a tube and that of a cell here quite coincide. The networks of cells which here form the system of tubes, terminate externally in the septa bounding the individual divisions, and we here see in close proximity considerable collections of spindle-shaped cells. In these cartilages, too, the whole mass of tissue is only connected by its exterior with the circulatory system; everything that penetrates into the interior must pass by a very circuitous route through a system of canals with numerous anastomoses, and the nutrition of the internal parts is altogether dependent upon this mode of conveyance. The semi-lunar cartilages are structures of considerable extent and great density, and, as they are entirely dependent for their nutrition upon this ultimate, minute system of cells, we have in them, much more than in cartilage, to deal with such an arrangement for the supply of nutritive juices, as cannot be under the direct control of the vessels.

For the sake of elucidation, I will merely add that the ultimate elements are seen to consist of very delicate cells, which are prolonged into fine filaments, that in their turn ramify, and look when cut across like small points in which a clear centre can be recognised. The filaments can ultimately be very distinctly traced back to the common cell just as in bone. They are extremely fine tubes which are intimately connected with one another, only that here they are in certain spots collected into large groups, by means of which the conveyance of the nutritive juice is principally effected, and that the intercellular substance in no instance becomes infiltrated with lime, but always preserves its character as connective tissue.

LECTURE V.

FEBRUARY 27, 1858.

NUTRITION, AND CONVEYANCE OF THE NUTRITIVE JUICES.

Tendons.-Cornea.-Umbilical cord.

Elastic tissue.-Corium.

Loose connective tissue.-Tunica dartos.

Importance of cells in the special distribution of the nutritive juices.

ALLOW me, gentlemen, as a supplement to what we saw and discussed in the preceding lecture, to lay before you a few more preparations in illustration of that peculiar species of nutritive arrangement which we have already seen to exist in various tissues, and which, I hope, will appear to you of very great importance in pathological processes also.

You will remember that the last object of our consideration was a ligamentous disc (Bandscheibe), as it occurs in its most marked form in the knee-joint in the so-called semilunar cartilages, which are really no cartilages at all. On the contrary, they possess the qualities of a flat tendon, and the individual structural relations which we found in them, are repeated throughout the whole of the transverse section of a tendon.

We have to-day a series of objects from the tendo

Achillis, both of the adult and the child, displaying the different stages of its development; and as this is, moreover, a tendon which is of importance in more than one way in an operative point of view, I may, I am sure, be excused for speaking a little more at length concerning it.

On the surface of a tendon we see, as you well know, with the naked eye, a series of parallel, whitish strie which run pretty close to one another in a longitudinal direction, and give rise to the characteristic glossy appearance. In a microscopical longitudinal section these striæ lie farther apart, so that the tendon presents a somewhat fasciculated appearance and looks less homogeneous than on the surface. This becomes much more evident in a transverse section, in

Fig. 37. Transverse section from the tendo Achillis of an adult. From the sheath of the tendon, septa are seen at a, b, and c, running inwardly, and uniting into a network so as to form the boundaries of the primary and secondary fasciculi. The larger ones (a and b) generally contain vessels, the smaller ones (c) do not. Within the secondary fasciculi is seen the delicate network formed by the tendon-corpuscles (reticulating cells-Netzzellen), or the intermediate system of juice conveying canals (Saftkanalsystem). 80 diameters.