550 FINE-STRUCTURE OF PROTOPLASMIC DERIVATIVES III 



A segments than in the B segments and that they unfold partially when 

 stretched. When collagen fibrils are stained with phosphotungstic 

 acid, the electron microscope reveals not merely one dark and one 

 bright segment per period, but a series of bands (e.g., 5) within the 

 dark segment. Apparently these bands combine preferentially with the 

 phosphotungstic acid. 



Suhmicroscopk structure of hones and teeth. Bone represents a complex 



system of collagen fibres, its inter- 

 fibrillar substance being calcified by 

 hydroxyl-apatite Caio(P04)6(OH)2 

 (Brandenberger and Schinz, 

 1945). It is a Wiener body, which 

 can only be imbibed, however, 

 with liquids of variable refractive 

 indices, if one of the two com- 

 ponents is destroyed. This can be 

 done either by decalcification or 

 by ignition of the organic com- 

 ponent. AscENZi (1950) has mea- 

 sured the form birefringence of 

 the organic substance (ossein) and 

 the inorganic substance. The re- 

 sult is represented in Fig. 175. The 

 ossein has almost no intrinsic bire- 

 fringence, whilst that of the incin- 

 erated bone is strongly negative. 

 This is due to the optical properties 

 of the hydroxyl-apatite which cry- 

 stallizes in optically negative hex- 

 agonal prisms. The minimum of 

 the rodlet birefringence curve at 

 n = 1.600 is caused by the optical properties of apatite (1.634 — 1.638 

 = — 0.004). 



In the electron microscope the collagen fibrils are visible with their 

 striation (Rutishauser, Huber, Kellenberger, Majno and Rouil- 

 LER, 1950; Huber and Rouiller, 195 i). 



Teeth have a similar submicroscopic structure to that of bones. Of 

 special interest is the enamel which covers the dentine as a specially 



0.009 



0.008 



0.007 



0.006 



0.005 - 



O.OOi, 



0.003 



0.002 



0.001 



001 



0002 



■ 0.003 



-0.00^ 



Fig. 175. Birefringence of human femoral 

 diaphysis (from Ascenzi, 1950). A) In- 

 organic bone fraction, B) ossein, C) total 

 bone. Abscissa: refractive index of the im- 

 bibition liquid. Ordinate: birefringence. 



