132 PHYSICAL CHEMISTRY IN MEDICINE. 



in that they themselves unite with the salt ions and form 

 aggregates without necessarily being precipitated, when 

 the size and charge of the particles, as in the case of 

 protein, are small. It is, for example, an easy matter 

 to show that by no means inconsiderable amounts of 

 barium sulphate, one of the least soluble of substances, 

 can be kept in solution in serum. If now, through the 

 metabolism of the cells, the dissolving colloids are de- 

 stroyed and not replaced, supersaturation and finally 

 precipitation of the crystalloidal material can easily be 

 brought about, after which, as is so often the case, crystals 

 that have once been formed may serve as centres for 

 further crystallization. This conception seems to make 

 clear the connection between crystallization and the vital 

 activities of the cells, as evidenced by the organization 

 of the supporting tissues. It renders intelligible also the 

 regularly observed phenomenon that a small portion of 

 colloidal material, which is no longer able alone to keep 

 the salts in solution, always crystallizes out with them. 

 In this same direction is to be sought the connection 

 between pathological processes of calcification, deposition 

 of uric acid, and tissue metabolism. If the beautiful 

 investigations of PAUL and His on the conditions deter- 

 mining the solubility of uric acid are not of that im- 

 portance for the pathogenesis of gout which they had 

 hoped, then this is dependent primarily upon the fact 

 that the same conditions of equilibrium which exist in 

 the organism in the presence of colloids were not estab- 

 lished in their experiment. 



A special problem is presented by the origin of the 

 great solidity of cartilage and bone, or rather their 

 peculiar colloidal intercellular substance. These tissues 



