144 THE CELL DOCTRINE. 



The Strxidure of Cells. — As to structure, cells have 

 been heretofore described as structureless, or vari- 

 ously granular, and with powers not exceeding 250 

 diameters, they may still be so described. Few cells 

 even with these powers are structureless, while on 

 the other hand, a highly granular condition of a cell 

 is considered indicative of some pathological change, 

 except in the case of nerve-cells, which in many 

 situations are admittedly highly granular in the 

 normal state. The same may be said of the nucleus. 

 Occasionally, however, even previous to 1867, certain 

 nerve-cells were described as striated in appearance. 

 Examples of structureless cells are most striking in 

 the unicellular organism, as the amoeba (Fig. 16, front- 

 ispiece), in which we have a structureless nucleated 

 mass, which owes whatever of structure it possesses 

 to foreign particles, which it takes up as food. So far 

 as the structure of the elementary part of the more 

 complex organisms, however, is concerned, the recent 

 discoveries, al ready described (see p. 11 7) as discernible 

 by a power as low as 300 diameters, demand a total 

 change in the description of the structure of cells. 

 Henceforward we must describe not only the nucleus 

 but also the cellular substance (protoplasm) as fibrillar 

 in structure, made up of a network of delicate fibres 

 the meshes of which are filled with an " interfibril- 

 lar " or " ground substance," which is structureless, 

 and that the fibrillse of the intracellular and intra- 

 nuclear networks afe continuous. And if Klein be 

 correct we must define the nucleoli as merely local 

 thickenings, natural or artificial, of the intranuclear 

 network. The intranuclear networks are much more 



