PROTOPLASM AND THE CELL 



27 



Structure of Protoplasm. — Protoplasm, when viewed under a high 

 magnification of a compound microscope, is a grayish, almost fluid mass, seem- 

 ingly almost devoid of any structure. A careful observer will, however, find 

 that the material seems to be made of a ground mass of fluid with innumer- 

 able granules of various size and form floating in the fluid portion. Other 

 observers believe protoplasm to consist of a fluid groundwork with in- 

 numerable tiny threads scattered through it, each thread being more or less 

 firmly united with other threads of the mass. Still other scientists hold that 

 protoplasm has essentially the structure of an emulsion or froth or foam. To 

 them the fine structure resolves itself into a collection of very minute bub- 

 bles. Doubtless all of the observers are right in part, for protoplasm doubt- 

 less assumes all of the above-mentioned forms in different plants and animals 

 and under different conditions. But we must also bear in mind that when 

 we make observations on protoplasm it may be already dead when we 

 examine it — and therefore undoubtedly greatly changed in structure — or 

 else we may view it under conditions which are far from the normal con- 

 ditions under which it usually exists as living matter. Finally, the instru- 

 ment we call the microscope, although seeming to be nearly perfect, may 

 not always give to our eye an exact representation of what is under its lenses. 



Cells of Various Sizes and Shapes. — 



Plant cells and animal cells are of very 

 diverse shapes and sizes. There are 

 cells so large that they can easily be seen 

 with the unaided eye; for example, the 

 root hairs of plants and eggs of some 

 animals. On the other hand, cells may 

 be so minute that in the case of the 

 plant cells we call bacteria, several mil- 

 lion could be placed on a dot of this 

 letter i. The forms of cells may be ex- 

 tremely varied in different tissues; they 

 may assume the form of cubes, col- 

 umns, spheres, fiat plates, or may be so 

 irregular that description is impossible. 

 One kind of tissue cell, found in man, 

 has a body so small as to be quite in- 

 visible to the naked eye, although it 

 has a prolongation several feet in length. 

 Such are some of the cells of the ner- 



~iJ n hfijf 



nmWk 



Animal cell, showing netlike 

 structure of the protoplasm. 

 (After Verworn.) 



