150 KERATIN AND KERATINIZATION 



attempt to demonstrate quantitatively the effects of competition between 

 follicles, An interfollicular competition for nutrient substance is immedi- 

 ately suggested by the most striking feature which emerges from the com- 

 parative study of the fleeces of the many domesticated sheep : viz. the fact 

 that the denser the fleece (fibres per cm 2 ) the finer and shorter are the 

 individual fibres. For quantitative data see Carter and Clarke (1957). 

 Fraser and Short (1960) have demonstrated also a negative correlation 

 between fibre size and the diameter and distance of adjacent fibres. See 

 also Ryder (1957). Fraser (1951) originally used the concept of com- 

 petition to explain the differences in the shape of the tip curl between 

 fibres formed by central and lateral primary follicles (Fig. 35), (p. 78). The 

 number of crimps in a periodic function of time (Norris, 1931, p. 156) and 

 a regular crimp of constant curvature will result if the growth rate is 

 constant. If the rate decreases, following on the initiation of adjacent new 

 follicles which compete for fibre forming substances, the curvature would 

 decrease and a sickle shaped tip would result, as is found on the primary 

 central fibre of a trio group. 



Fraser's original proposals (1951) were clear-cut and offered plausible 

 suggestions relating growth rates, tip shapes and order of appearance of 

 wool fibres during development. The subsequent attempt to evaluate 

 these theories quantitatively by statistical analysis of the data has led to 

 some secondary elaboration which makes it difficult to test them ex- 

 haustively as once envisaged. Such concepts as : competition for space in 

 early development and variations in a genetically-determined " efficiency 

 of competition " on the one hand, and actual histological findings of 

 secondary follicles having different origins — directly from the epidermal 

 surface and by budding from existing follicles on the other — have intro- 

 duced complexities. Fraser and Short (1960) are now of the opinion that 

 more information concerning the performance of the individual follicle 

 must be obtained. In fact, Rudall (1956) (p. 73) has already shown that 

 it is the dimensional structure (diameter, surface area and height) of the 

 papilla which is most strongly correlated with the follicle output and the 

 dimensions of the fibre. Presumably it is these papillary dimensions which 

 are influenced directly by competition and other controlling factors. 

 Considerations of this sort, which promise to relate follicle output to the 

 activity of the actual cells covering the papillary surface by supplementing 

 the statistical approach, are likely to lead to a clearer understanding of the 

 growth process in general. See also Burns and Clarkson (1949). 



Patterns of hair growth and control 



Hair growth and replacement varies in different animals and is a species 

 characteristic; within a species the sex hormones in particular determine a 

 masculine and feminine pattern which disappears after gonadectomy. The 



