CHANGES WROUGHT IN PATHOLOGY. 13* 



In both cases we have to do with a solidification of their 

 surfaces which makes the emboli behave, in spite of their 

 gaseous or liquid character, like solid obstructions to the 

 circulation. 



In a new light appear also, through a study of the 

 colloids, the extracellular phenomena observed in the 

 development of solid supporting substances, such as car- 

 tilage and bone, and the precipitation of crystalloidal sub- 

 stances in the tissues connected with them. The latter 

 question, which is also of great pathological importance, 

 has aroused much interest in the past decade, but it does 

 not seem to have been possible to get far beyond the 

 recognition of the difficulties which the solution of the 

 problem encounters. The nucleus of the question seems 

 to lie in the fact that we are dealing, on the one hand, 

 with simple processes of crystallization, while, on the 

 other hand, formative influences on the part of the cells 

 and functional adaptations to the forces destined to act 

 upon them seem to be clearly discernible in the arrange- 

 ment of the crystallization. Besides the studies of nu- 

 merous investigators on the process of ossification, it has 

 been BIEDERMANN, more especially within recent years, 

 who, through his excellent work on the shells of molluscs, 

 crustaceans, and insects, has furnished much important 

 experimental material. 



The importance of colloidal chemistry in these prob- 

 lems evidences itself at once in that first and most important 

 question of the conditions under which the scarcely 

 soluble salts are kept in solution and precipitated in 

 suitable places. The colloids constitute, as shown by 

 many experiments, an excellent means under certain 

 circumstances of keeping slightly "soluble salts in solution, 



