8 KERATIN AND KERATINIZATION 



and Robson (1955) (Table 1(b)) and those quoted by von Bergen (1954) 

 (Table 1 (c)) all of samples of wool, and by Schroeder and Kay of 

 feathers (1955) (Table 2). Although it contains older and less reliable 

 data, Table 3, taken from Ward and Lundgren (1954), is valuable in that 

 it permits a comparison between several varieties of keratin. The question 

 of the significance of the differences between the figures given, even for an 

 apparently homogeneous material such as wool, will be discussed later 

 (p. 31). 



Table 2. Amino Acid Composition of White Turkey Feather Parts and of 

 Goose Feather Barbs and Goose Down.* 



(Values are in terms of g of amino acid per 100 g of moisture- and ash-free 



material.) 



* Data taken from Schroeder and Kay (1955). 



f For an explanation of the parts of a feather see p. 30. 



Even when the chemical composition of a fibrous macromolecular 

 material is known, its detection and characterization in cells and tissues 

 may offer difficulties in routine histochemistry. For some materials 

 reliable histochemical tests have been developed (see p. 29); others 

 are recognized more or less negatively, simply by their fibrous character 

 and their intractable behaviour towards the usual stains and reagents. 



