772 FRANCIS H. McCRUDDEN 



The theories of functional inertia and allergy cited here are, of course, 

 not used as arguments in favor of the conception of normal and patho- 

 logical bone metabolism outlined in this chapter. This conception is based 

 upon the facts observed in chemical, clinical, and anatomical investiga- 

 tion. The analogies are cited merely to show that, in all probability, the 

 process in osteomalacia is but a special example of certain more general 

 laws governing the modus operandi of living matter. 



II. Diseases of the Joints 



For practical use in discussing the metabolism, the principal chronic 

 arthropathies may be classified as follows: 



1. True gout. 



2. Trophic arthropathies secondary to disease of the central 

 nervous system. 



3. Arthropathies secondary to infections. 



4. Primary hypertrophic arthritis. 



5. Primary atrophic arthritis. 



Only a relatively small proportion of chronic arthropathies are seen 

 that cannot be easily classified according to this scheme: (a) those cases 

 that do not appear to come under one of these headings at all ; (b) those 

 cases which it is difficult to classify. Most of the difficulty arises from 

 the fact that some cases of atrophic arthritis in the early, active stages 

 resemble certain forms of the infectious type of arthritis. If these cases 

 are followed long enough, the course of the disease usually shows whether 

 they belong in class 3 or class 5. 



The metabolism in the first type of arthropathy true gout is dis- 

 cussed elsewhere in these volumes. 



The metabolic disturbances in the arthropathies of severe nervous dis- 

 ease, the second type, affect chiefly the bone adjacent to the articulating 

 surfaces proper. In the section on bone metabolism it is pointed out 

 that bone is continuously undergoing metabolism, that old bone is con- 

 tinuously being absorbed and new bone laid down, and that the new bone 

 laid down may not exactly resemble the old either in chemical composition, 

 density, or architectural structure. When there is a great need of lime 

 salts in other parts of the body, there may be a change in the chemical 

 composition of the newly apposed bone ; it may become poor in calcium. 

 In wasting diseases, or when a limb has been immobilized in a plaster 

 cast, or after paralysis, the density of the bone may change, leading to 

 rarefaction, disuse atrophy. Deformities or other changes leading to alter- 

 ation in the direction of stresses or of strains may be followed by changes 

 in the architectural structure. All these changes are in the nature of 



