CELL STRUCTURE 47 



inorganic salts are present in the cell by virtue of both physical and 

 chemical influences, some simply (Hffusiii^; in and out, others com- 

 bining with the proteins and being held chemically. 

 Bechhold summarizes his conception of cell walls as follows: 

 "Every cell at its surface possesses a membrane which is dependent 

 upon the composition of the interior of the cell. This membrane 

 may be visible and may have been formed through the gelatinizal ion of 

 the cell protoplasm at the periphery. It may, on the other hand, be so 

 thin as to be invisible, being formed by the concentration and spread- 

 ing out of such albuminous and fatty colloids as diminish the surface 

 tension of the cell content at the interface. The cell membranes, de- 

 veloping as a result of the gelatinization of cell protoplasm, are at 

 first, in youth, expansile and elastic; with increasing age these mem- 

 brane colloids, depending upon their environment and upon chemical 

 influences, or as a result of mere colloid aging phenomena, become poor 

 in water and lose their elasticity." 



The intercellular substance varies greatlj^ in different tissues. In the case of 

 the supportive tissues it is the important element, and the cells seem to exist chiefly 

 for the purpose of forming and keeping it in repair as it is worn out. In the epi- 

 thelial and secreting tissues, however, the intercellular substance is reduced to a 

 minimum, except in so far as a cement substance is required, and the cells generally 

 lie in almost immediate apposition. It is probable that there is a greater or less 

 amount of cement substance, even between the most closely applied cells, and this 

 substance seems to be related to mucin. It can generally be brought out by stain- 

 ing with silver nitrate, and Macallum^^ points out that this reaction is merely a 

 micro-chemical test for chlorides, and indicates that the cement substance con- 

 tains them in larger proportion than does the cytoplasm. 



" Proceedings of the Royal Society, 1905 (76), 217. 



