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little doubt that it is justifiable to extend this theory to the 

 explanation of its intimate structure also. It is true that 

 the protoplasm swells up under certain solutions in the same 

 way as the cell-wall does, and hence we may conclude that it 

 also is built up of minute solid particles, separated by areas of 

 fluid ; but as to their form, shape, and size we are at present 

 entirely ignorant except in this one particular that they do not 

 act on polarized light in such a manner as to suggest that they 

 are crystalline. 



Next we have to consider the general properties of a cell. If 

 we cut a thin section of some colored portion of a plant — e.g., a 

 beet-root — and place it under the microscope, we can observe in 

 each cell the cell-wall, protoplasm, nucleus, and cell-vacuole, in 

 which latter we find contained a bright red-colored fluid, which is 

 the cell-sap, in this case colored red. If such a section is left in 

 water for some time, nothing particular will be found to take place ; 

 all the parts will retain their position. We have, then, a vesicle 

 containing red coloring matter which is soluble in water placed 

 in water, yet the red fluid does not escape from the cell into 

 the water. If we repeat the experiment by placing some red 

 fluid on an animal membrane, and then floating the latter on 

 water, the red fluid will soon be found to dialyse — i.e., pass 

 through the interstices between the solid particles of which the 

 membrane consists, from the exterior into the water. What 

 prevents, then, the same result in the previous experiment with 

 the beet-root ? We would find, if we were to leave the section 

 for days and weeks in water, that no escape of fluid would 

 take place, and an escape of fluid would only occur when the 

 entire disintegration of the cell by bacteria — or, in other words, 

 its death — occurred also. The cells of the beet-root, then, 

 though placed in water, are still living, not dead, and it is only 

 when they become dead that the red fluid contained in them 

 escapes through the cell-walls. If, however, another section be 

 plunged for a few minutes into strong spirit, when it is after- 

 wards immersed in water the red fluid escapes directly through 

 the wall, proving further that this property of retention depends 

 on the life of the cell. The only living part of the cell is the 



