CHEMICAL CONSTITUTION OF THE ANIMAL BODY. 145 



Coagulated proteids are soluble only in strong acids and 

 alkalies. 



Classification and Distinguishing Characters of Proteids. 



1. Native albumins : Serum albumin ; egg albumin ; solu- 

 ble in water. 



2. Derived albumins {albuminates) : Acid and alkali albu- 

 min ; casein ; soluble in dilute acids and alkalies, insoluble in 

 water. Not precipitated by boiling. 



3. Globulins : Globulin (globin) ; paraglobulin ; myosin ; 

 ■ fibrinogen. Soluble in dilute saline solutions, and precipitated 



by stronger saline solutions. 



4. Peptones : Soluble in water ; diffusible through anima 

 membranes ; not precipitated by acids, alkalies, or heat. De- 

 rived from the digestion (peptic, pancreatic) of all proteids. 



5. Fibrin : Insoluble in water and dilute saline solutions. 

 Soluble, but not readily, in strong saline solutions and in dilute 

 acids and alkalies. 



CERTAIN NON-CRYSTAlliINE BODIES. 



The following bodies are allied to proteids, but are not the 

 equivalents of the latter in the food. 



They are all composed of C, H, N, O. Chondrin, gelatin, 

 keratin have, in addition, S. 



Chondrin : The organic basis of cartilage. Its solutions set 

 into a firm jelly on cooling. 



Gelatin : The organic basis of bone, teeth, tendon, etc. Its 

 solutions set (glue) on cooling. 



Elastin: The basis of elastic tissue. Its solutions do not 

 set jelly-like (gelatinize). 



Mucin : From the secretion of mucous membranes ; precipi- 

 tated by acetic acid, and insoluble in excess. 



Keratin : Derived from hair, nails, epidermis, horn, feathers. 

 Highly insoluble. 



Nuclein: Derived from the nuclei of cells. Not digested 

 by pepsin ; contains P but no S. 



THE FATS. 



The fats are hydrocarbons ; are less oxidized than the carbo- 

 hydrates ; are inflammable ; possess latent energy in a high 

 degree. 



Chemically, the neutral fats are glycerides or ethers of the 

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