CHEMICAL COMPOSITION OF THE TISSUES. 77 



fat, certain extractive matters and salts (chlorides of sodium and potas- 

 sium), which may be obtained by evaporating the alcoholic solutions, 

 and would then have to be separated by special processes, and be 

 weighed. The undissolved residuum, now acted on by boiling water, 

 will yield to that fluid more extractive matters, and more salts (chiefly 

 phosphates of soda and potash), which would have to be separated 

 and weighed. The residue this time (insoluble in either ether, alco- 

 hol, or water), would consist chiefly of an animal substance, which 

 would be found to be of an albuminoid nature, mixed however with 

 earthy constituents. It would have again to be dried at 212 to expel 

 the water, and then be weighed. This dried mass being now burnt in 

 a covered vessel, the loss would indicate the quantity of albuminoid 

 matter, whilst the ashes would consist of the earthy salts (phosphates, 

 carbonates, and sulphates of lime and magnesia), which would finally 

 have to be separated by ordinary chemical processes, and be weighed. 

 In this way, all the proximate constituents of the white brain-sub- 

 stance, and their relative quantities, would be, though, after all, 

 roughly ascertained. 



We shall now briefly indicate the chemical constitution of the vari- 

 ous tissues, reserving to special occasions the details of the composi- 

 tion of the different secretions. 



The connective tissues, areolar, fibrous, tendinous, and membranous, 

 including the basis of the skin, contain about two-thirds of water, and 

 one-third of solid matter. The solid matter is nearly entirely resolved 

 into gelatin on being boiled, but, like the blood itself, contains traces 

 of alkaline and earthy salts. 



Permanent cartilage contains about three-fifths of water and two- 

 fifths of solid matter, which is resolved into chondrin on boiling. The 

 solution gelatinizes on cooling, perhaps from the presence of a little 

 gelatin. This cartilage contains from 3 to 4 per cent, of alkaline 

 and earthy salts, chiefly carbonate and sulphate of soda, and carbon- 

 ate of lime, but it also contains chloride of sodium and phosphate of 

 magnesia and lime. Temporary cartilage yields a solution of ehondrin, 

 which does not gelatinize. 



The fibro-cartilages have a mixed composition, yielding both gelatin 

 and chondrin on being boiled. The yellow elastic tissue is said to 

 contain less water than the other soft tissues. It offers great resist- 

 ance to the action of boiling water, but at last yields, together with 

 some gelatin, a peculiar substance named elastin, unlike both gelatin 

 and chondrin ; about one-half, however, is insoluble. 



Recent bone contains nearly 10 per cent, of water. The animal 

 part of dried bone constitutes 33 per cent., or one-third of its weight, 

 and is convertible into gelatin on being boiled. The remaining two- 

 thirds, or 66 per cent., are inorganic or mineral matters, and consist 

 of 51 parts of tribasic phosphate of lime (or bone-earth), and 11 

 parts of carbonate of lime (chalk) ; the rest (a very small proportion) 

 is fluoride of calcium (fluorspar), phosphate of magnesia, and chloride 

 of sodium (common salt). The compact bony substance contains 

 more earthy matter than the spongy bone ; and also proportionally 

 more phosphate to the carbonate of lime than the latter. In old age, 



