A Biomolecular Survey of Calcification 113 



This feature of interchange of mineral with respect to the organic composition of 

 the tissue is best illustrated by first comparing a range of structures based on one 

 type of calcium salt and then examining analogous structures with two different types 

 of mineral deposit. In Fig. 1 the X-ray powder diffraction photographs have been 

 arranged to compare four subjects, each of which contains crystalline inorganic 

 deposits closely resembling bone salt; the four examples are chosen from different 

 phyla (two invertebrate, two vertebrate) and each is associated with a different 

 molecule. Fig. 1 a is the diagram from the tip of the dorsal spine of the Channel 

 Catfish, Ictalarus punctatHS. This subject, though of lower vertebrate origin, is 

 typical of bone and contains collagen as the principal organic component. On the 

 other hand, the specimen in Fig. 1 b from Sei whale (Balaenopterus horealis) baleen 

 contains crystallites of bone salt essentially similar to those found in Fig. 1 a, but in 

 this case the organic component is keratin and collagen is absent (Pautard, 1965). 

 In Fig. 1 c and 1 d, the inorganic salt closely resembles that in Fig. 1 a and 1 b, but 

 the main organic component in both cases is the polysaccharide chitin, in the r/-form 

 in the case of the chela of the Mantis Shrimp Squilla in Fig. 1 c and probably in the 

 />-form in the case of the shell of the brachiopod Lingula unguis in Fig. 1 d. 



Analogues structures often contain mixtures of calcium salts, but in some cases 

 one or another crystalline species predominates, occasionally in adjacent tissues. This 

 is particularly true in the keratins, where bone salts have been demonstrated 

 crystallographically, but where "amorphous" calcium deposits, probably of carbonate 

 as well as phosphate, have been suggested (Pautard, 1963). Fig. 2 a shows a quadrant 

 X-ray diffraction pattern of Sei whale baleen. The fibre axis is vertical and the 

 c-axis of the hydroxyapatite crystallites (judging from the meridional disposition of 

 the 002 reflexion) is generally parallel to the axis of the «-helices (shown by the 

 orientation of the reflexion at about 5.1 A on the meridian). On the other hand the 

 diffraction diagram of the tip of the anterior dorsal papillae of the tongue of a bull 

 (Fig. 2 b) shows "spotty" reflexions of calclte, suggesting crystals of large (about 

 1 micron) size not oriented with respect to a-hellces. Close Inspection of the original 

 diffraction pattern shows a second series of unorlented reflexions corresponding to the 

 apatite spaclngs in Fig. 2 a. In Fig. 2 c, the crystallographic pattern from the chela of 

 Squilla closely resembles that from the Sei whale baleen fibre In Fig. 2 a, but there Is 

 no evidence for any orientation of the crystallites with respect to the axis of the 

 appendage, which is vertical. In Fig. 2 d, a similar structure — the chela of the small 

 crab Callinectes found In the same area as the shrimp In Fig. 2 c gives an unorlented 

 diffraction pattern of calclte of smaller crystal size than the comparable salt In 

 Fig. 2 b. Thus, In one set of comparisons, we have large and small crystals of calclte 

 and apatite, oriented and unorlented and as discernable mixtures In two analogous 

 subjects, both of epidermal origin, containing keratin in one case and r/-chitin in 

 the other. 



From the above, and from other, comparisons It Is apparent that the mineral 

 phase and the organic phase are not linked by the specific nature of the calcium salt 

 and the protein or the polysaccharide framework. At least, this cannot be true In the 

 gross sense, for where there are oriented fibrous macromolecules there can usually be 

 found also oriented crystallites of one salt and another. The term "matrix", which 

 is customarily assigned to collagen in bone, tends to be misleading when applied to 

 the organic moiety of other forms of calcification. Collagen is a relatively homo- 



