26 THE CELL 



e. Uniformity of Protoplasm. Diversity of the Cell. 



A great uniformity of appearance is manifested by protoplasm 

 in all organisms. With our present means of investigation we are 

 unable to discover any fundamental difference between the proto- 

 plasm present in animal cells and that in plant cells, or unicellular 

 organisms. This uniformity is of necessity only apparent, being due 

 to the inadequacy of our methods of investigation. For since 

 the vital processes occur in each organism in a manner peculiar 

 to itself, and since the protoplasm, if the nucleus be excepted, is 

 the chief site of the individual vital processes, these differences 

 must be due to differences in the fundamental substance, that is to 

 say, in the protoplasm. We must therefore accept, as a theory, 

 that the protoplasm of different organisms varies in its material, 

 composition and structure. Apparently, however, these important 

 differences are due to variations in molecular arrangement. 



In spite of the uniform appearance of the protoplasm, the in- 

 dividual cell, of which after all the protoplasm forms only a more 

 or less important part, when taken as a whole, may vary very 

 much in appearance ; this is due partly to variations in external 

 form, but chiefly to the fact, that sometimes one, and sometimes 

 another substance is stored up in the protoplasm, in such a manner 

 as to be distinguishable from it. Sometimes this occurs to so 

 great a degree that the whole cell appears to be composed almost 

 entirely of substances which under other circumstances are not 

 present in protoplasm at all. If we imagine that these substances 

 have been eliminated, a number of larger and smaller gaps would 

 be naturally produced in the cell, between which the protoplasmic 

 groundwork of the cell would be seen as partition walls and frame- 

 works, which are sometimes extremely delicate. This arrangement 

 of the protoplasm, as has been already mentioned (p. 19), must 

 not be confused with the network structure, which, according to 

 the opinion of many investigators, is inherent to protoplasm itself, 

 and which was more fully described in the chapter on the structure 

 of protoplasm. 



The names deutoplasm (van Beneden) and paraplasm (Kupffer, 

 II. 24) have been proposed for these adventitious substances. 

 Since, however, the idea of an albuminous substance is always con- 

 nected with the word plasm and these substances may consist of 

 fat, carbohydrates, sap, and of many other bodies the use of the 

 above terms does not seem desirable, and it is better either to class 

 them generally as intraplasmic products and adventitious cell contents 



