108 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



albumen is formed at the same time. The same changes follow prolonged 

 boiling with dilute sulphuric acid. There are some grounds for supposing 

 that chondrin is not an individual albuminoid, but that it is rather a 

 mixture of gelatin, mucin, and salts, since its general characteristics are 

 similar to what might be possessed by a combination of these bodies. 

 All the connective tissues, therefore, possess a body which may be 

 transformed into gelatin by boiling, and a cement substance, mucin. 



_The following statements represent in a few words the distinctive 

 characteristics of mucin, chondrin, gelatin, and albumen: — 



Mucin. — Precipitated by acetic acid, the precipitate is not dissolved 

 by sodium sulphate. 



Chondrin. — Precipitated by acetic acid, the precipitate is dissolved 

 by sodium sulphate. Precipitated by lead acetate, alum, silver nitrate, 

 and copper sulphate. 



Gelatin. — Not precipitated by acetic acid, nor by acetic acid and 

 potassium feirocyanide, nor by lead acetate. 



Albumen. — Dissolved by acetic acid, the solution is precipitated by 

 potassium ferrocyanide, or by the addition of alkaline salts and heat. 



Gelatin and chondrin are mostly to be recognized by their hot 

 solutions forming a jelly when cooled. This, as already mentioned, is not 

 invariably the case, as the property is lost by prolonged boiling, or by 

 boiling with acids. 



Closely allied to these collagenous albuminoid constituents of the 

 connective tissues we meet with two other albuminoids which have many 

 points in common with the above, with the exception that they do not 

 form jellies when their solutions cool. These two bodies are Elastin, 

 obtained from elastic tissue, and Keratin, a nitrogenous body of epithelial 

 origin. 



3. Elastin. — Elastin is the albuminoid principle contained in yellow 

 elastic tissue. When yellow elastic connective tissue is boiled with 

 water, after mucin has been removed, collagen is dissolved. The residue 

 which remains is mainly composed of elastin. Elastin may be prepared 

 by macerating the ligamentum nuchse of the ox with ether, and then hot 

 alcohol, to remove the fats ; boiling water, to remove collagen and convert it 

 into gelatin, and 10 per cent, caustic soda, and then acetic acid, allowing 

 the boiling in water to continue for at least thirty-six hours, and in the 

 acetic acid for at least six hours. After being subjected to the soda, the 

 remaining tissue is again boiled with dilute acetic acid, well washed with 

 water, and afterward the acid neutralized. After washing with hot 

 water a brittle, yellowish mass is obtained, which recovers its elasticity 

 and fibrous appearance if soaked in dilute acetic acid. 



Elastin is insoluble in cold or boiling water, and offers remarkable 

 resistance to chemical agents, unless boiled for a very long time. It is 



