GENERAL ANATOMY. /I 



pass between the surrounding medium and the contents 

 of the cell ; the character of the membrane and of the cell- 

 sap must determine the condition of the diffusion-currents, 

 and thereby also the functional character of the cell ; the 

 different appearance of tissues is chiefly conditioned by the 

 fact that the cells, spherical in the beginning, change their 

 form ; in the case of fibrillar connective tissue, for example, 

 they increase enormously in length and become fine fibrillae. 

 Since the life of an organism is nothing else than the co- 

 operation of all its cells, they flattered themselves that 

 through the cell theory and the discovery, brought about 

 by it, of the physical unity of the animal and vegetable 

 body they had made an important advance in the great 

 problem of the physical explanation of the phenomena of 

 life. Cell genesis also seemed, according to the theory, to 

 be just as satisfactorily explained on a mechanical basis as 

 the formation of a crystal. In the " cytoblast " the nuclear 

 bodies, nuclear membrane, and cell membrane must be 

 formed by precipitation just as in the process of crystalliza- 

 tion. 



Reform Movements. Since that time our conception 

 of the character of cells has completely changed. The cell 

 does not, after the manner of a crystal, arise as a new 

 formation in a matrix, but it presupposes the existence of 

 a living mother-cell, from which it arose by division or 

 budding. Just so also the cell is not a physical unit, but 

 is itself an organism which shows to us all the enigmas of 

 life, the physical basis of which our investigations must 

 ever keep in view as a goal, though it be still indiscernibly 

 distant. The membrane and cell-sap are of quite sub- 

 ordinate importance for the character of the cell ; rather 

 the most important thing in it is the previously dis- 

 regarded substance, for which H. von Mohl introduced the 

 name protoplasm. According to the newer conception 

 the cell is practically a small Imnp of protoplasm, usually, 

 perhaps ahvays, provided witJi one or more nuclei. This 

 newer conception of the character of a cell has developed 

 so gradually, and has so slowly supplanted the Schleiden- 



