6 ANIMAL PROTEINS 



of aluminium, chromium and iron, and of mercuric chloride, 

 zinc sulphate, ammonium sulphate, potassium carbonate, 

 acidified brine. Many of these precipitations have analogies 

 in leather manufacture (see Parts I. to IV.). The gelatin 

 peptones or gelatoses are formed by hydrolysis with acids, 

 alkalies, ferment or even by digestion with hot water only. 

 A more detailed description of the properties of gelatine is 

 given in Part V., Section I. Gelatine is sometimes called 

 " glutin " and " ossein." 



Animals are much the most important source of proteins, 

 especially of those which are of importance in industrial 

 chemistry. Proteins occur in nearly every part of all 

 animals, and the " protoplasm " of the living cell is itself 

 a protein. The keratins include the horny tissues of 

 animals : the epidermis proper, the hair, horns, hoofs, 

 nails, claws, the sebaceous and sudoriferous glands and ducts, 

 and also the elastic fibres. The gelatins are obtained from 

 the collagen of the skin fibres, the bones, tendons, ligaments, 

 cartilages, etc. Fish bladders yield a strong gelatin. The 

 albumins are obtained from the ova, blood, lymph, muscles 

 and other internal organs of animals. 



The classification of proteins herein adopted fits in well 

 with the scope and purpose of this volume. The keratins 

 are of little importance in chemical industry, but are of 

 immense importance in mechanical industry, e.g. the woollen 

 trade, which is based upon the keratin comprised by sheep 

 wool. The collagen of the hide and skin fibres is of vast 

 importance to chemical industry, and is the basis of the 

 extensive leather trades discussed in Parts I. to IV. The 

 waste pieces of these trades, together with bones, form the 

 raw material of the manufacture of gelatin and glue, as 

 discussed in Part V. The proteids of animals' flesh and 

 blood, milk and eggs form the source of the food proteins 

 discussed in Part VI. The food proteins embrace chiefly 

 albumins, but gelatins and even keratins are involved to 

 some extent. 



