112 CHEMICAL COMPOSITION OF ANIMAL TISSUES. 



Its power of forming a jelly on cooling is such, that a solution of one 

 part in 100 of water will become a consistent solid. And its reaction 

 with Tannic acid is so distinct, that the presence of one part of Gelatine 

 in 5000 of water is at once detected by infusion of Galls. There can 

 be no doubt that Gelatine does not exist exactly as such in the Fibrous 

 tissues ; since none can be dissolved out of them by the continued action 

 of cold water, and it usually requires the prolonged action of hot water, 

 to occasion their complete conversion. There are some substances, how- 

 ever, in which this is not requisite ; and from which the -gelatine may 

 be extracted within a shorter time. This is the case, for example, with 

 the air-bladder of the Cod and other fish; which when cut into shreds 

 and dried, is known as Isinglass. It is the case also with the substance 

 of bones, from which the calcareous matter has been removed. In both 

 instances it would seem that the state of organization is very imperfect ; 

 the fibrous structure being by no means well-marked. When the fibrous 

 arrangement is more complete, the solubility of the tissue is much di- 

 minished. Hence it would seem that the particles have a different ar- 

 rangement in the tissues, from that which they have in the product 

 obtained by boiling. Their ultimate composition, however, is the same ; 

 for when any serous membrane, or other tissue principally composed of 

 the white fibrous element, is analysed by combustion, the elements are 

 found to have the same proportion to each other as in Gelatine, allow- 

 ance being made for the small admixture of other substances. The 

 action of Tannic acid, too, is the same on the organized tissue, as it is 

 on the gelatine extracted from it ; and hence results its utility in pro- 

 ducing an insoluble compound, not liable to undergo decomposition, in 

 the substance of the Skin, converting it into leather. 



176. It is not yet known how Gelatine is produced in the Animal body. 

 There can be no doubt that it may be elaborated from Albumen ; since 

 we find a very large amount of Gelatine in the tissues of young animals, 

 which are entirely formed from albuminous matter ; and also in the 

 tissues of herbivorous animals, which cannot receive it in their food, as 

 Plants yield no substance resembling gelatine. Carnivorous animals, 

 however, will receive it ready formed, as part of their aliment. There 

 is no reason to believe that it is capable of being converted into Albu- 

 men ; and consequently it can never be applied to the nutrition of the 

 albuminous tissues. If Gelatine be boiled for some time in caustic potash, 

 it is decomposed, with an escape of ammonia ; and two new compounds, 

 leucine, and glycocoll or gelatine-sugar, are generated. The production 

 of leucine from Gelatine, by the action of the same reagent as that 

 which caused its generation from Albumen, is a fact of much importance ; 

 as showing that, notwithstanding their difference of composition and 

 characters, a certain similarity in the arrangement of their ultimate 

 elements still subsists between these two bodies. Glycocoll is an organic 

 base of great interest from its relations to other substances ; as will be 

 shown hereafter. It has a strong sweet taste, and is very soluble in 

 water, from which it may be crystallized like ordinary sugar. Its compo- 

 sition is comparatively simple ; being 4 Carbon, 4 Hydrogen, 1 Nitrogen, 

 3 Oxygen. 



177. A peculiar modification of Gelatine, which presents itself in 



