528 TISSUES OF THE CONNECTIVE SUBSTANCE. 



The quantity of organic substance in the bones, calculated from the 

 loss of weight in burning, varies between 300 and 520 p. m. This 

 variation may in part be explained by the difficulty in obtaining 

 the bony substance entirely free from water and partly by the very 

 variable amount of .blood-vessels, nerves, marrow, and the like in different 

 bones. The unequal amounts of organic substance found in the com- 

 pact and in the spongy parts of the same bone, as well as in bones at 

 different periods of development in the same animal, probably depend 

 upon the varying quantities of these above-mentioned tissues. Dentin, 

 which is comparatively pure bony structure, contains only 260-280 

 p. m. organic substance, and HoppE-SEYLER 1 therefore thinks it probable 

 that perfectly pure bony substance has a constant composition and 

 contains only about 250 p. m. organic substance. The question whether 

 these substances are chemically combined with the bone-earths or only 

 intimately mixed has not been decided. 



The nutritive fluids which circulate through the bones have not been isolated 

 and we only know that they contain some protein and some NaCl and alkali 

 .sulphate. 



Bone Marrow. We differentiate between the red and yellow mar- 

 row, to which also belongs the gelatinous marrow poor in fat found in 

 fat atrophy and in old age. The difference between the first two-men- 

 tioned kinds of marrow lies, essentially, in the fact that the red marrow 

 contains a greater quantity of erythrocytes besides a higher content of 

 protein and less fat. The fat of the yellow marrow is, according to 

 NERKiNG, 2 richer in oleic acid and poorer in solid fats than the fat of the 

 red marrow. Besides the fat, lecithin also occurs in the bone-marrow 

 and this varies in amount in different animals and at various ages, as 

 mentioned on page 235. The protein consists of a globulin coagulating 

 at 47-60 C. (FORREST) and a nucleoprotein with 1.6 per cent phos- 

 phorus (HALLIBURTON 3 ) besides fibrinogen (P. MULLER*), traces of 

 albumin and proteose. In the extractives are formed lactic acid, inosite, 

 hypoxanthine, cholesterine and bodies of an unknown kind. The quan- 

 titative composition of both kinds of marrow varies considerably with 

 the fat content, and the reports of the different investigators are corre- 

 spondingly discrepant (NERKING, HUTCHINSON and MACLEOD 5 ). 



The diverse quantitative composition of the various bones of the 

 skeleton depends probably on the varying quantities of other tissues, 



1 Physiol. Chem., 102-104. 



2 Bioch. Zeitschr., 10. 



3 Forrest, Journ. of Physiol., 17; Halliburton, ibid., 18. 



4 See footnote 1, p. 245. 



5 Nerking, 1. c.; Hutchinson and Macleod, Journ. of Anat. and Physiol., 36. 



