THEODOR SCHWANN 265 



that might be precipitated while passing through it, is not deposited. 

 The second vesicle, when it is developed at all, must needs be de- 

 veloped relatively with more rapidity than the first ; for as the solution 

 is in the most concentrated state at the beginning, the necessity for 

 the formation of a second layer then occurs sooner ; but when it is 

 formed, the concentration of the fluid is diminished, and this necessity 

 occurs either later or not at all. It is possible, however, that even a 

 third, or fourth, and more, may be formed ; but the outermost layer 

 must always be relatively the most vigorously developed ; for when the 

 concentration of the solution is only so strong, that all that must be 

 deposited in a certain time, can be deposited in the outermost layer, it 

 is all applied to the increase of this layer. 



Such, then, would be the phenomena under which substances ca- 

 pable of imbibition would probably crystallize, if they did so at all. I 

 say probably, for our incomplete knowledge of crystallization and the 

 faculty of imbibition, does not as yet admit of our saying anything 

 positively a priori. It is, however, obvious that these are the princi- 

 pal phenomena attending the formation of cells. They consist always 

 of substance capable of imbibition ; the first part formed is a small cor- 

 puscle, not angular (nucleolus), around this a lamina is deposited 

 (nucleus), which advances rapidly in its growth, until a second lamina 

 (cell) is formed around it. This second now grows more quickly and 

 expands into a vesicle, as indeed often happens with the first layer. 

 In some rarer instances only one layer is formed ; in others, again, 

 there are three. The only other difference in the formation of cells is, 

 that the separate layers do not consist of the same chemical substance, 

 while a common crystal is always composed of one material. In in- 

 stituting a comparison, therefore, between the formation of cells and 

 crystallization, the above-mentioned differences in form, structure, and 

 mode of growth fall altogether to the ground. If crystals were 

 formed from the same substance as cells, they would probably, in 

 these respects, be subject to the same conditions as the cells. Mean- 

 while the metabolic phenomena, which are entirely absent in crystals, 

 still indicate essential distinctions. 



Should this important difference between the mode of formation 

 of cells and crystals lead us to deny all intimate connexion of the two 

 processes, the comparison of the two may serve at least to give a clear 

 representation of the cell-life. The following may be conceived to be 



