COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 57 



It thus appears that the offal contained relatively more pro- 

 tein and water and less ash and fat than the carcass. From the 

 weights of the carcass and offal, respectively, may be computed 

 the percentage distribution of the ingredients between the two 

 with the results shown in Table 12, from which it appears 

 that on the average 39 per cent of the protein, 28 per cent of 

 the ash and 23 per cent of the fat of the entire animal was 

 contained in the offal. 



Epidermal tissues 



91. Functions. The epidermis, or outer, layer of the skin, 

 consists of numerous layers of cells of which those nearer the 

 true skin are alive and capable of multiplication while towards 

 the outer surface they are gradually transformed to flattened, 

 horny scales which serve as a protective layer and gradually 

 slough off. Both the epidermis and the protective covering of 

 animals, hair, wool, feathers, etc., as well as the hoofs 

 and horns, corresponding to the nails in man, are modified forms 

 of epidermal tissue, their characteristic ingredients being the 

 class of albuminoids designated as keratins (51 e). 



92. Composition. Except for their high and variable sul- 

 phur content, the keratins differ little in elementary composi- 

 tion from the simple proteins, but they are much more resistant 

 to chemical reagents, being, for example, insoluble in alkalies in 

 the cold and unattacked by either pepsin or trypsin. These 

 properties fit them well for the outer covering of the animal. 

 The following table shows the elementary composition of some 

 of the more important epidermal tissues : 



TABLE 13. COMPOSITION OF EPIDERMAL TISSUES 



