12 Prof. H. Karsten on the Development of the Organic Cell, 



is often difficult to discover in this plant, yet such is the fact; 

 whilst the majority of naturalists, without it, acknowledging the 

 general application of the law of analogy, will not suppose that, 

 in the simplest processes of organization, nature follows totally 

 different courses. 



The primitive form which matter capable of organization 

 assumes is that of the vesicle — the cell, inseparably composed 

 of membrane (wall) and contents. Each of these two consti- 

 tuents of the elementary organ, constantly exerting the most 

 intimate influences upon each other, is capable of advancing 

 further in its development by the aid of the physico-chemical 

 forces to which it is indebted for its existence. 



The membrane of the cell grows, but not by passive exten- 

 sion as a consequence of endosmose of its fluid contents. It is 

 rather itself engaged in a constant, although, in fact, almost 

 imperceptible, change of the quantity and nature of the matter 

 composing it, assuming peculiar forms, very probably dependent 

 upon the nature of this material, as I have in some measure 

 shown in the preceding pages and in several other contributions. 



The fluid contents of the cell have also their own peculiar 

 powers of development. Whilst the cell-wall shows this by its 

 enlargement, and usually laminated thickening, the fluid con- 

 tents manifest it by the production in them of secretion-cells, of 

 transient duration. 



Indeed, as the assimilative faculty of the cell-wall gives rise to 

 the formation of progressively higher combinations, the soluble 

 products of which become finally dissolved in the general 

 nutritive fluid, so, by the agency of the same faculty, secre- 

 tion-cells make their appearance in the fluid contents of tissue- 

 cells at certain periods of their development. These transient 

 secretion-cells serve for the maintenance of the cells of a 

 secondary, tertiary, and succeeding generation, which originate 

 in the cell-juices, are developed at the cost of the absorbed 

 secreted matters, and serve for the reparation of the primary 

 cell and the maintenance of the cell-individual. This formative 

 process within the cell is not restricted, under certain con- 

 ditions of nutrition, to the regeneration of the individual cell, 

 but from the cell-contents rich in formative material several 

 new cells, of the nature of the reproducing mother cell, are 

 simultaneously produced, having for their object the multiplica- 

 tion of the tissue-cells. 



Owing to this complicated structure of the tissue-cells which 

 enter into the composition of developed organisms, it is erroneous 

 to speak of unicellular plants and animals. With as little 

 i-eason can we imagine cells without membranes ; such bodies, 

 in my opinion, should be designated drops or granules. 



