82 THE ACTION OF ENZYMES 



Many proteins are precipitated as a coagulum or 

 insoluble clot when their solutions are boiled. 



They are also peculiar in behaving both as acids or 

 bases. Some of them, such as casein, have the acid 

 character most strongly marked, and form neutral salts 

 with alkalis, while in others the basic properties are most 

 obvious. In aL, however, both properties are present in 

 greater or less degree. 



It is necessary to note here that much confusion exists 

 in regard to the nomenclature used for the proteins and 

 their derivatives. The term proteid is very often used in 

 this country as equivalent to protein, but in Germany it 

 has a more restricted meaning, being applied to a special 

 group of proteins mentioned below ; if used at all it 

 should be applied in the latter sense, and brought into 

 line with continental asage. Proteins are not infrequently 

 spoken of as albumens by some writers, and in France 

 they are described as " substances albuminoides." The 

 older school of chemists have kept the word albuminoid 

 as a term for proteins in general, speaking of albuminoids 

 of milk, feeding cake, etc., while physiologists have 

 habitually used it for a small class of proteins, of which 

 gelatine of bone and keratin of horn are representatives. 



2. The classification and nomenclature of the proteins 

 is still in a transition state, and will need revision from 

 time to time to bring it into harmony with the advances 

 made in the knowledge of the chemical and physical 

 constitution of these substances. The following classes 

 and names are those at present recommended by a 

 committee of the Chemical Society of London : 



(i) Protamines. These are strongly basic bodies, 

 obtained chiefly from the spermatozoa of fishes, and are 

 among the simplest proteins. They are not coagulated 



