METABOLISM IN DISEASES OF BONES AND JOINTS 773 



reflex responses to local needs, and, like other reflex responses, will fail to 

 function properly if the reflex arc is anywhere broken. This gives the 

 clue to the nature of the changes in the joints in disease of the central 

 nervous system. The structure and density of the bone about the joints 

 is determined by the character of the stimuli coming from the joints. 

 In tabes, the arc connecting these deep centripetal impulses with the 

 corresponding centrifugal impulses is interrupted. The changes found 

 in the Charcot joints of tabes are such as we should predict; the bone be- 

 comes soft and rarefied and structureless; it disappears from where it 

 should be present, and appears in the form of osteophytic outgrowths 

 where it should not be present. Bone metabolism is going on, but neither 

 the density nor the structure is determined by the local needs ; the metab- 

 olism is "running wild." This lack of order or system in the metabolism 

 applies also to the soft parts about the joint ; the articular surfaces may 

 disappear. The changes in syringomyelia are probably of the same gen- 

 eral nature. 



The third type of chronic arthritis includes not only those cases sec- 

 ondary to known infection in other parts of the body, but also many 

 cases in which no infection can be discovered. The latter group of cases 

 are put in this class, because they present the clinical characteristics which 

 are typical of recognized secondary infectious arthritis. The pathological 

 process in the joints may be due to the action of bacteria in the joints 

 or to toxins absorbed from foci or infection elsewhere. In some cases it 

 is possible that the metabolism of the joints is affected indirectly through 

 the action of toxins on the central nervous system. No metabolism studies 

 in this type of arthritis are on record in the literature. 



The fourth type of chronic arthritis is seen in middle aged people. 

 It affects one or two, or a few joints only, and is not progressive. There 

 is no increase in the joint fluids, the joint slits are well preserved in 

 radiograms, and there is little or no periarticular swelling. There is 

 thickening and lipping, with ultimate ossification of the edges of the 

 cartilage which can be felt on palpation and seen in X-ray plates. 



The fifth type of chronic arthritis is seen in adults of any age. While 

 only a few joints may be actively affected at any one time, the disease is 

 progressive and usually spreads until most of the joints become involved. 

 In the early stages there is an increase in the joint fluids, and X-ray 

 plates show disappearance of the joint slits. In the early stages the 

 periarticular structures are swollen and infiltrated, giving the joints a 

 spindle shaped appearance. These swellings are soft and elastic. In the 

 later stages, after absorption of the exudate, the joints become smaller, 

 owing to atrophic changes in the cartilage (seen in radiograms). Later, 

 the joints become deflected and subluxated; and muscular atrophy, bone 

 atrophy, and atrophy of the skin and nails appears. 



