Protein — Non - Proteids 69 



nic acid, as for instance, when the skin of an animal 

 is treated with an extract of hemlock or oak bark, the 

 result is a substance which does not putrefy, and which 

 gives to a tanned hide the properties of leather. 



Keratin and similar substances . — The hair, wool, 

 hoofs, horns, and feathers are made up chiefly of 

 a compaund which bears the name keratin. Chemi- 

 cally, it is closely related to the true proteids, we may 

 believe, because when treated with heat or with chemi- 

 cals like acids and alkalies, the resulting products are 

 nearly similar to those that are secured in the same 

 ways from albumins. Sulphur is a much more promi- 

 nent constituent of keratin than of the native pro- 

 teids, the analyses of human hair showing as high as 

 5 per cent, the average amount found in horn being 

 3.30 per cent. These keratin bodies belong usually to 

 the epidermis or outer skin of the animal, and are 

 modifications of the exterior tissue to serve certain 

 distinct purposes where rigidity or wearing quality is 

 necessary. 



PROTEIN — THE NON - PROTEIDS 



There are certain nitrogen compounds included in 

 the term protein which are non-proteid in character, 

 that is, they possess physical and chemical properties 

 greatly removed from those which characterize albumin 

 and other true proteids. Their office as nutrients is 

 also less comprehensive than that of the albuminoids. 



One group of non -proteids which we speak of under 

 the general term amides, is found chiefly in plants. 



