138 ANIMAL SUBSTANCES. 



them their nutritious qualities. When evaporated 

 to dryness, it forms portable soup, size, glue, &c. 

 The union of this latter substance in the skin with 

 tannin constitutes leather. Isinglass is gelatine 

 procured from certain parts of several fish, particu- 

 larly the sturgeon. The tendons and membranes of 

 the body are chiefly gelatine. 



Fibrin, or animal jibre, forms the basis of the 

 muscular, or fleshy parts of animals. It is there 

 combined with albumen, and remains with it after 

 all the soluble parts of the flesh have been separated 

 by water. It may also be obtained from blood, by 

 washing the clot or coagulum in water, till a white 

 fibrous matter remains. Fibrin is not soluble in 

 cold water, but is very slightly so iri boiling water. 

 It is soluble in acids and alkalies, and by its union 

 with the latter a soap is formed. Chaptal em- 

 ployed this property to make a soslp from wool. 

 It is very analogous to vegetable gluten. 



Albumen is the principal constituent of the serum 

 of blood, and is also called coagulable lymph. The 

 white of eggs consists almost entirely of albumen. 

 It is miscible with cold water, but is coagulated by 

 heat, which forms the best test of its presence. 

 It is also coagulated by acids and alkohol. 



Mucus. This substance in animals appears in- 

 tended to lubricate or smooth certain parts of the 

 body, and seems very analogous to a solution of 

 gum. However, Dr. Bostock has shown 1 that it 

 differs from gelatine, as it cannot in cold water be 

 brought to assume the gelatinous state. Tannin 

 precipitates gelatine, but not mucus, whereas sub- 

 acetate of lead, (extract of Goulard,) forms a preci- 

 pitate with mucus, but not with gelatine. Mucus 

 is found in saliva, tears, in the intestines, joints, &c. 



