KATE OF KEjrVENATION OK THE SKELETOX 19" 



fuystals ol' (lentinr and bono is ubout 10 " cm.; while the very efi'ectively mi- 

 neralized enamel contains larger crystals (10~^ cm.). It is, therefore, quite pro- 

 bable that the difference in the extents of mineralization of the epiphysis and 

 diaphysis manifests itself in a moderate difference in the sizes of the ultimate 

 crystals in the two types of bone tissue. It is of interest to note that the diffoience 

 in hardness of the different types of bones is, to a laige extent, the result of a 

 different degree of orientation of the crystallites of the bone. X-ray patterns in- 

 dicate that orientation occurs during growth and first in those bones where the 

 need for solidity (e.g. leg bones) is greatest [Caglioti and Gigante, ]93()]. 



summary 



Labelled (radioactive) phosphate was administered to rabbits and frogs lepeal- 

 edly during the experiment in order to keep the radioactive plasma inoiganic 

 phosphorus at a constant activity level. The comparison of the activity of 1 mgni 

 bone inorganic P with that of the plasma inorganic P permits us to conclude to 

 what extent the mineral constituents of the bone were renewed during the expe- 

 riment. 



Within oU da_\s, 30% of the femur and tibia epiphysis weie found to be renewed, 

 while the corresponding figure for the diaphysis amounted to 7%. Half 

 of the mineral constituents of the scapula were found to be unchanged. The phos- 

 phatides of the bones and the marrow were entirely renewed. 



The phosphorus of the apical part of the dentine of the labbit's incisor was 

 found to have the same activity as the plasma phosphorus. From this result il 

 follows that this part of the dentine was grown with the participation of labelled 

 plasma phosphorus during the experiment. The greater part of the incisal end of 

 the dentine was not formed by a calcification process in situ but by a '\slip" of 

 the apical part of the dentine. 



The same behaviour is shown even more pronouncedly by the enamel. No 

 interaction of any significance takes place between the incisal part of the enamel 

 and the dentine either during their formation or at a later date. The atoms pre- 

 sent in the former are to a veiy large extent those which weie proA'iously located 

 in the apical (medial) part of the enamel. 



References 



Armstrong (1940) J. hiol. Chein. (in the Press). 



Artom, Sarzana and Segre (1938) Arch. int. Physiol. 47, 245. 



Bale, Hodge and Warren (1934) Amer. J. Roentgenol. 32, 369. 



Caglioti (1936). Atti Congr. naz. Chim. pura appl. 1, 320. 



Caglioti and Gigante (1936) B. C. Accad. Lincei, Classe sci. /is. 23, 878. 



Chievitz and He\t}sy (1935) Nature, Lond., 136, 754. 



Chievitz and Hevesy (1937) Kgl. Danske Vidensk. Selsk. Biol. Medd. 13, 9. 



COHN and Greenberg (1939) J. hiol. Chetn. 128, 116 and 130, 625. 



Cook, Scott and Abelson (1937) Froc. nat. Acad. Sci. 23, 528. 



DoLS and. Jansen (1937) Froc. Acad. Sci. Amst. 40, 3. 



Does, Jansen, Sizoo and Van der AIaas (1939) Froc. Acad. Sci. Amst. 42, 2. 



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13, 1. 

 Lefevre and Baee (1939) ./. biol. Chem. 129, 125. 

 Paneth (1922) Z. Elcktrochcm. 28, 113. 



