CELLS. 59 



stance might be produced within and excreted from it ; or, like rennet 

 upon casein, it might act upon the protein combinations in the cjto- 

 blastema, in such a manner that they should coagulate where in contact 

 with it ; or lastly, by the extraction of the alkali it might render an 

 albuminous substance insoluble, as is the case in the development of 

 Ascherson's vesicles. Which of these various possibilities really obtains, 

 must at present remain undetermined, yet, for my own part, I should 

 prefer the first view, in order to retain one and the same condition, a 

 physical one, for all the different modes of cell-development. 



I do not think it necessary to enter at greater length, in the present 

 place, into this very obscure subject, and I will therefore only once 

 more express my opinion, that I hold the physical processes of cell- 

 development, which may pass under the general name of molecular at- 

 traction, to be something quite different from those which attend crystal- 

 lization. Although in both, solids arise out of fluids, and grow by the -; 

 further agglomeration of molecules, yet in cell-development different 

 substances are as a rule superimposed, plane geometrical solids are never 

 formed, and the process is always limited in the same way, after the 

 formation of the cell-membrane. Since organic and even histogenetic 

 substances are crystallizable, the reason of cell-development is not to be 

 found in permeability nor in any of the other properties of organic com- 

 pounds, which in fact, even if the substances did not crystallize, would 

 not suffice to explain all the peculiarities of cells in question, nor their 

 power of self-division and multiplication ; but in those peculiar, as yet 

 unknown combinations of the powers of nature which are concerned in 

 organic development. To discover these is the further and difficult 

 task of Histology, w^hich to this end must be wholly directed to the so- 

 called molecular forces of organic forms, especially to those electrical 

 phenomena which must indubitably occur in the cells as well as in their 

 derivative structures, the nerve-tubes and muscular fibres.* 



§ 14. Vital Phenomena of the Perfect Cells. Gfroivth. — The cells, 

 when once completed, perform a considerable number of functions, which 

 relate as well to the form of the whole cell and of its contents, as to their 

 chemical composition, and are called growth and change of substance. 



• [The essential distinction between living organized matter (tlie cell) and mere inorganic 

 formed matter (the crystal) api)ears to us to be here overlooked. If some inorganic substance 

 should be discovered crystallizing in the form of nucleated cells, it would not the more ap- 

 proximate to an animal or vegetable cell ; for the essential character of the latter, which 

 is its passage through a definite succession of slates and not its form merehj, would still be absent. 

 It is this characteristic peculiarity of organized living beings, which has been exhibited 

 widi so much force by Alex. Braun, in the plant, under the somewhat fanciful title of ' Ver- 

 jungung' (rejuvenescence), but which equally obtains in the animal. The crystal tends to 

 attain a permanent condition, the cell towards its own disappearance, either by death or 

 division. The crystal tend.s towards an equilibrium with the forces around it, the cell 

 incessantly disturbs that equilibrium, — life and change being one. — Trs.] 



