METABOLISM IN DISEASES OF BONES AND JOINTS 735 



believed to be newly made bone free from inorganic material. Cohn- 

 heim(&) was the first to express doubt concerning the correctness of 

 this conception of the process. According to Cohnheim, the bones, even in 

 the adult, are undergoing active anabolism and catabolism. In osteo- 

 malacia, when bone is destroyed, organic substances as well as lime salts 

 are taken up by the osteoclasts, and then, just -as in rickets, new bone 

 made up of the organic matrix, but free from or poor in lime salts, is 

 laid down. Evidence supporting either of these two opinions was not 

 available at the time Cohnheim wrote. 



Normal Bone Metabolism. The conception that the mineral constit- 

 uents of the body are dead, are not a part of the living body, and are not 

 undergoing metabolism is a remnant of the old idea that there is a sharp 

 distinction between the living or organic elements or compounds and the 

 inorganic, an idea rejected long ago. During the past two decades many 

 investigations, especially those of Loeb, have demonstrated incontestably 

 that calcium and certain other inorganic elements are as much a part of 

 "living" tissue as nitrogen, hydrogen, and oxygen. We do not have any 

 difficulty in understanding that the small amounts of calcium, magnesium, 

 and iron in the blood or muscles are used up that is, catabolized and 

 excreted and have to be renewed, in other words, undergo metabolism; 

 and it is difficult to understand why the pathologists who took Virchow's 

 view could find difficulty in believing that the mineral salts of the bone 

 undergo metabolism. If the muscle cells with their fraction of one per 

 cent of mineral salts undergo metabolism, then why not also the bone cells 

 with their fifty or sixty per cent mineral salts ? We have no difficulty in 

 understanding that the material of the blood plasma, or the connective 

 tissue, or neuroglia fibrils must be renewed (Haidenhain). Why should 

 there be any difficulty in understanding that the quite analogous bone 

 should be renewed? A priori then, we should say that bone normally 

 undergoes metabolism. 



But there is more direct evidence of both bone anabolism and bone 

 catabolism. 



We have structural evidence of bone metabolism in the interlacing 

 osseous plates of cancelli, which, depending on the direction of strain, 

 are sometimes laid down in vertical columns, sometimes in oblique abut- 

 ments. When as the result of accident or growth the strains and stresses 

 change, the old material is absorbed and new material laid down, evidence 

 of the metabolism being seen in the shifting of the lines of the cancelli to 

 conform to the new pressure requirements (Schwatt). These alterations 

 in minute structure, continuously adapting structure to function, are reflex 

 changes under control of the nervous system. In response to centripetal 

 impulses, set up by the pressure stimuli in the joints and bones, and 

 passing to the central nervous system, centrifugal impulses controlling the 

 bone metabolism pass back. If the nervous mechanism breaks down, the 



