CELLS AND THE CELL THEORY 



31 



Structure. When protoplasm is examined under the micro- 

 scope it is not found to be a homogeneous jelly, as was at first 

 thought, but to have an intricate structure which is only partly 

 disclosed by the microscope; Fig. 11. The exact structure of 

 this cell substance has not been fully determined, and there 

 are at least three different theories to explain its microscopic 

 appearance. 



The Reticular Theory. One school of scientists describes pro- 

 toplasm as an extremely minute network of fibers forming a sort 

 of sponge, in the meshes of which 

 there is found a moving liquid; 

 Fig. II A . This is the so-called 

 reticular or fibrillar theory of pro- 

 toplasmic structure. 



The Foam Theory. Another 

 school explains the appearance 

 of protoplasm as due to a mass 

 of minute bubbles, like soapsuds 

 on a small scale; and insists that 

 what appear to be fibers are only 

 the delicate lines separating the 



bubbles from each other; Fig. 11 B. This is the foam theory of 

 protoplasmic structure. 



The Granular Theory. Still a third theory suggests that the 

 protoplasm consists of an indefinite number of minute, living, 

 moving granules, arranged in lines resembling fibers or in various 

 other figures. This is the granular theory of protoplasmic 

 structure. 



Between these theories the scientists have not reached any 

 conclusion, although the first two have been more generally 

 accepted than the last. It is quite possible, and even probable, 

 that all of the theories may have a certain amount of truth in 

 them, and that protoplasm does not in all cases have the same 

 structure. It is certain, however, that protoplasm always shows 

 a structure and is not a homogeneous body. In most cases 



A B 



FIG. 11. DIAGRAMS ILLUSTRAT- 

 ING THEORIES OF PROTOPLASM 

 A, the Fibrillar; B, the Foam. 

 (Dahlgren and Kepner.) 



