32 CELLS AND EXTRACELLULAR ELEMENTS. 



there is in cells a large field of structural factors that is beyond 

 our powers of observation. If we could penetrate within this 

 invisible field, we might find much of histologic and structural 

 organization that would be of the greatest interest and im- 

 portance in explaining the mysteries of vital phenomena. 

 But we cannot as yet penetrate it, and the various vital struct- 

 ures and units which eminent biologists have assumed as 

 entering into the structure of cells, such as the hypothetical 

 pangenes, plasomes, plastidules, biophors, determinants, and 

 the like, have at present little more than a speculative value. 



Extracellular elements: The non-cellular, intercellular, or 

 extracellular constituents of tissues serve to connect, support, 

 and provide a mechanical framework for the cells, which of 

 themselves do not possess the firmness requisite for a large 

 organism. These elements are not the seat of any real vitality, 

 which pertains exclusively to the cells ; they are produced by 

 the vital activities of the latter. 



The intercellular substances exhibit considerable variety, 

 and in different tissues occur in varying proportions to the 

 total amount of the cells. 



The simplest form is the intercellular cement, a scanty sub- 

 stance which cements cells together. The plasma of the blood 

 and the serum of lymph may be regarded as a fluid intercel- 

 lular substance in which the cells are suspended. 



The greatest variety and quantity of extracellular elements 

 occur in the connective tissues, where the fibres, the hyaline 

 matrix of cartilage, and the mineral matter deposited in bones 

 are of this character. 



