112 



F. G. E. Pautard 



Organic phase 

 It is unfortunate that the extensive investigation of bone collagen over the past 

 few years has tended to obstruct serious survey of the nature of other organic sub- 

 stances associated with calcium salts in biological tissues. An almost universal pre- 

 occupation with collagen structure and chemistry has obscured the fact that there are 

 numerous subjects which contain bone salts associated with other proteins and with 

 polysaccharides. Even in enamel, where it has been suggested on chemical (Eastoe, 

 1960) and crystallographic (Pautard, 1961) grounds that collagen might be absent, 

 the heterogeneous nature of the sparse organic phase has left us with the possibility 

 that collagen-like proteins, or macromolecules with some features in common with 

 collagen, might play a direct part in calcification. From considerations of bones and 

 teeth alone it is not easy to divorce collagen entirely from some specific association 

 with calcium phosphate, but if we look at the wider panorama of calcification we 

 find that there is no evidence for a close association of any one calcium salt with any 



Fig. 1. X-ray powder diffraction diagrams (CuR a radiation) from four subjects each containing calci 

 phosphate, a. Tip of dorsal spine of Ictalunis piinctatus. b. Fringe fibre tip of baleen from BuLtoioptc 

 borealis. c. Tip of chela of SqiiilLi species, d. Shell of Llng:i!a unguis 



one organic substrate and no real grounds for assuming that the "choice" of a 

 particular calcium salt for a particular structure is connected with the nature of the 

 fibrous macromolecules which are present. 



