300 SPECIAL HISTOLOGY. 



boiling under an increased pressure, the gelatine is separated from the 

 calcareous salts. 



The physical properties of the bones correspond with their composi- 

 tion. Their hardness, density, and rigidity are due to the earthy, 

 whilst their elasticity and flexibility depend upon the organic constitu- 

 ents. In the normal bone of the adult, the two principal constituents 

 are united in such proportions, that the bones, together with consider- 

 able hardness and rigidity, have a certain degree of elasticity, though 

 slight, so that they possess a considerable resisting power, and are 

 broken, though not very readily, by the application of greater mechani- 

 cal force. At an earlier age, when the cartilage is in greater relative 

 proportion, the hardness of the bones is much less, their sustaining 

 power consequently less considerable, and they are more liable to be 

 bent ; whilst on the other hand, owing to their greater elasticity, they 

 are much less liable to be broken. This is the case in a much higher 

 degree in rachitis, in which morbid condition, the organic constituents 

 amount to from 70 to 80 per cent. A condition the reverse of this is 

 observed in old age, when the bones, though certainly harder, are more 

 brittle, and therefore more readily fractured, to which liability, however, 

 the rarefaction of the tissue which takes place in consequence of age, 

 partly contributes. The inflammability of bone depends upon its 

 organic basis, and its capability of resisting putrefaction to the inor- 

 ganic constituents. The latter being so intimately combined with the 

 animal tissues, serve as a protection to them, so that bones from ancient 

 burial-places, and those of fossil animals still retain the full proportion 

 of cartilage. 



The true cartilages, even in the foetus, contain, in their organic basis, 

 from 50 to 75 per cent, of water, 3 to 4 per cent, of salts (chiefly of 

 soda and carbonate of lime, and also some phosphate of lime and mag- 

 nesia). The organic basis has been hitherto supposed to consist entirely 

 of chondrin, a substance allied to gelatin, soluble in boiling water and 

 gelatinising as it cools; but it was noticed by Bruns (p. 216), that the 

 matrix and the cells of cartilage were not equally soluble in water, and 

 Mulder and Donders have rendered it probable that the chondrin, which 

 had hitherto been investigated, is not a simple substance, and that the 

 cartilages consist of several bodies of different natures, the matrix, and 

 the membranes of the parent cells, their contents, and the secondary 

 cells, of which the first is more soluble in water, potass, and sulphuric 

 acid, than the others. 



The fibro-cartilages (cartilages containing connective tissue) have 

 been, as yet, but little investigated. J. Muller, in the interarticular 

 cartilages of the knee of the Sheep, found no chondrin ; whilst Donders, 

 on the other hand, met with it in the intervertebral ligaments (" Holl. 

 Beitr.," p. 264) ; he did not determine whether they also contained 

 gelatin. According to Virchow, the gelatinous, nuclear portion of these 



