TISSUES, ORGANS, AND SYSTEMS. 79 



tions ; appearing, firstly, as a simple parenchyma composed of cells ; and 

 secondly, as a cellular tissue, with an intermediate substance or matrix 

 between the elements. The cartilage-cells present little peculiarity in re- 

 spect of form ; they are generally round or elongated, frequently flat- 

 tened or fusiform, very rarely stellate (in Cuttle-fishes and Sharks, 

 and in enchondroma). Their membrane is ordinarily thick, frequently 

 invested by concentric laminae ; the contents are clear and more fluid, 

 with a single nucleus, and, though not constantly, with one or many fat 

 globules. The interstitial substance is either homogeneous or finely 

 granulated or fibrous, even with clear separable fibres. The chemical 

 characters of cartilage are in some respects but little known. It is 

 ascertained, however, that the cells and the intermediate substance are 

 composed of different substances. The membranes of the cartilage cells, 

 in fact, are not dissolved by boiling, and offer a lengthened resistance to 

 alkalies and acids, peculiarities which distinguish them from the sub- 

 stances which yield gelatine, but approximate them to elastic tissue. 

 The contents of the cells coagulate in water and dilute acids, and are 

 readily dissolved by alkalies. The interstitial substance is, in most car- 

 tilages, chondrin, and only in the reticulated cartilages is it a substance 

 closely allied to that of the elastic tissue. Consequently the cartilages, 

 which consist only of cartilage cells, yield no gelatine upon boiling, and 

 its occurrence is no essential character of cartilage. Physiologically, 

 the solidity and elasticity of the cartilages are particularly to be noted, 

 as by these properties it is fitted for its various uses. In growing carti- 

 lages the change of material is very energetic ; they constantly contain, 

 in certain localities, numerous bloodvessels in peculiar canals; and, as I 

 have demonstrated in the nasal cartilage of the calf, even nerves. Their 

 growth takes place, firstly, by endogenous multiplication of cells, traces 

 of which are always clearly to be observed in perfect cartilages ; and 

 secondly, by the deposition between the cells, which originally exist 

 alone in all cartilages, of an interstitial substance from the blood-plasma, 

 which, according to Schwann, at first yields no chondrin even in the 

 true cartilages, and subsequently gradually increases in quantity. In 

 perfect cartilages the nutrition is by no means energetic ; and it has, 

 apart from the vessels of the perichondrium which invests many carti- 

 lages, and those of the neighboring bone, no particular agent, except in 

 the cartilages (septum of the nose) of a few mammalia, and in the pla- 

 giostome fishes, in some of which last, according to Leydig, even in old 

 individuals, vascular canals exist (Raja\ in others anastomosing, fusi- 

 form, or stellate corpuscles (Sharks). With age, the intermediate sub- 

 stance of certain true cartilages readily becomes fibrous, and very similar 

 in its chemical characters to that of the reticulated cartilage, which de- 

 monstrates that these two kinds of cartilage are not widely separated ; 

 the true cartilages also not uncommonly ossify, vessels, cartilage, and 



