36 CHEMICAL CONSTITUENTS : GELATIN, CHONDRIN. 



same is the case with the animal substance of bones from 

 which the earthy matter has been removed ; and in each case 

 the fibrous texture of the living tissue is but very imperfectly 

 developed. For the extraction of gelatin from the skin, the 

 ligaments, the tendons, and various internal membranes, 

 whose fibrous texture is more pronounced ( 29), a much 

 longer action of boiling water is required. 



20. A peculiar modification of gelatin, which presents 

 itself in Cartilage (or gristle), is distinguished as Chondrin. 

 This requires longer boiling than gelatin for its solution in 

 water; as is seen when a knuckle of veal or of mutton 

 is cooked, the tendons and ligaments about the joint 

 being almost reduced to pulp, whilst the cartilages are scarcely 

 at all softened. The essential properties of chondrin are 

 nearly the same as those of gelatin, and its composition 

 seems nearly identical; but it is thrown down from its 

 solution by muriatic and acetic acids and some other reagents, 

 which do not disturb a solution of gelatin. 



21. It is not yet fully known how the material of the 

 gelatinous tissues is produced in the animal body. There 

 can be no doubt of its being producible from albumen ; since 

 we find it in large proportion in the tissues of animals that 

 have never received gelatin into their bodies in any shape. 

 And although carnivorous animals will receive it as part of 

 their aliment, yet there is strong reason to believe that the 

 gelatin which is thus supplied to them does not really serve 

 to nourish their bodies, but that it is speedily decomposed 

 and got rid of ( 159). It maybe considered as quite certain 

 that the albuminous tissues cannot be formed by the meta- 

 morphosis of gelatin ; whilst conversely, looking to the fact 

 that in the egg and in milk no gelatin is provided for the 

 young animal, although the gelatinous tissues form a yet 

 larger proportion of its body than they do in the adult, we 

 seem entitled to question whether it is possible that these 

 tissues can be formed in any other way than at the expense 

 of the albuminous constituents of the blood. 



Structure of the Primary Tissues. 



22. In considering the structure of the " primary tissues," 

 of which the various organs of animals are composed, it will 

 be convenient first to treat of those which are subservient 



