The Microscope. 141 



Schleiden had regarded this membrane as a mucilaginous zone ;; 

 but von Mohl in answer to Schleiden says : " The question at 

 issue is not one concerning mere words. A peripheral layer, 

 which is differentiated, more dense than the internal protoplasm,. 

 and capable of folding itself so as to involve also the cellular 

 contents, presents without doubt, all the characteristics of a true 

 membrane." 



In speaking of the vacuoles and the fluid they contain, he callS' 

 this fluid " cell-sap," and he states expressly, in accordance with 

 Dujardin (as above cited), that we must not mistake this fluid 

 for the protoplasm. He says : " This (the protoplasm) is re- 

 pelled by the cell-sap and sometimes reduced into threads which 

 break and contract towards the periphery where the whole proto- 

 plasmic mass will form a sac enclosing a large vacuole filled with 

 water, i. e., cell-sap. These vacuoles, therefore, are nothing but 

 inclusions." 



According to von Mohl the grains of starch, of aleurone and 

 crystals, etc., are only inclusions contained in the protoplasmic- 

 mass, but entirely distinct from it.^ 



We may sum up the statements of von Mohl in the following 

 words : The vegetable cell is a closed utricle surrounded by a 

 solid membrane, containing a protoplasmic body in which is- 

 lodged a nucleus. With regard to the protoplasm itself, we 

 must distinguish a peripheral part, which is difl'erentiated intO' 

 a primordial membrane, and the internal part, which in young 

 cells is homogeneous, but in mature cells is sometimes reduced 

 to mere threads by inclusions, or even it may form a sac close- 

 to the cellular membrane. 



Von Mohl goes still further. Convinced, as he was, that in- 

 Cytology every term must receive a meaning he is careful to de- 

 termine precisely what must be attributed to the word protoplasm, 

 " In general," he says in 1846, " this word is used to signify that 

 opaline and viscous mass which exists prior to the parts of the cell;; 

 and in fact, it is this protoplasm which furnishes the materials 

 out of which are formed the primordial utricle and nucleus."" 

 Thus he characterizes living matter. Later however, in 1851, 

 when he treats ex prqfesso, of the cellular organization, having 



1 Prof Carnoy introduces two terms to represent the inclusions of von Mohl. He- 

 reserves the term inclusion for foreign substances introduced into the cell, as water^ 

 Diatoms^ etc., and he gives the name mclavata to those substances formed in the cell 

 by the protoplasm, such as starch, aleurone, etc. 



