GELATIN— CIIONDRIN. 25 



all the animal fluids yield an extract to water, wliicli strongly 

 resembles, if it be not altogether identical with, ptyalin. 



Diagnosis. Ptyalin may be distinguished from the protein- 

 compounds by its indifference to ferrocyanide of potassium ; and 

 from pepsin by its non-precipitation by dilute acids. 



7. Gelatiri — Chondrin and Glutin. Under the term gelatin 

 we include the organic tissue of bone, cartilage, sinew, ligament, 

 skin, cellular tissue, and serous membrane. All these substances 

 dissolve by long continued boiling in water, and the solution on 

 cooling assumes a consistent gelatinous mass. It is represented 

 in various degress of purity by glue, size, and isinglass. Gelatin 

 does not exist as gelatin in the animal tissues, but is formed 

 from them by the action of boiling water. IMiiller has shown 

 that there are two (if not three) distinct forms of gelatin. To 

 that which is obtained from the permanent cartilages, the cornea, 

 fungous bones, &c. the term chondrin is given, while glutin in- 

 cludes those forms of gelatin which are obtained from skin, 

 serous membrane, hoof, bone, tendon, fibrous and spongy carti- 

 lage, cartilage of bone, &c. As chondrin and glutin differ not 

 only in the sources from which they are derived, but also in 

 many of their chemical characters, we shall consider them 

 separately. 



Chondrin is most easily obtained by boiling any of the per- 

 manent cartilages, as for instance those of the ribs, larynx, or 

 joints, for about twenty-four hours, in water : the solution must 

 then be strained, in order to remove any coagulated matters, and 

 allowed to gelatinize ; it must then be di'ied at a low heat. 



In this state it is hard and brittle, colourless and transparent. 

 It sinks in cold water, and swells very much, without dissolving. 



Scherer has deduced from his analyses the following formula^ 

 for chondrin, C^^^ H^^ Ng O^^, which corresponds numerically 

 with P^ + 4 HO + 0^.2 



Its formula, according to Mulder, is Cg^^ H^g^ N^^ O,^^ S, or 

 20 (Cjg H,3 N^ 0.) + S. When burned it leaves about 4^ of 

 phosphate of lime. 



Chondrin is precipitated from its solution, and notredissolved in 

 an excess of the test, by acetic acid, tannin, the neutral and basic 



' See AppendLv I, Note 13. ^ Deduced from Liebig's formula. 



