96 BIOLOGY: GENERAL AND MEDICAL 



In the larger free cells, such as amoeba and paramcecium, 

 we find granules (physodes) of temporary occurrence 

 which are probably the not yet utilized products result- 

 ing from the intracellular digestion of the smaller entities 

 upon which the organisms feed. 



In vegetable cells there is even less difficulty in differ- 

 entiating certain large coarse granules not essential 

 components of the cytoplasm, yet contained in that sub- 

 stance and destined for the performance of definite 

 functions. These are the chromatophores, which are 

 the antecedents of the chloroplasts, by which chlorophyl 

 is formed, and the chromoplasts by which are elaborated 

 the pigments by which the flowers and fruits are colored. 

 Plant cells also contain starch and aleurone granules in 

 many cases. Many plant cells are also distended with 

 sap which takes the form of vacuoles that soon become 

 too large to be mistaken for granules. 



It is thus seen that the cytoplasm is not only granular 

 because of its spongioplasm, but also because of adventi- 

 tious granules constituting the deutoplasm or paraplasm, 

 matters temporarily contained in it. 



It must, however, occur to the student that there is 

 no criterion for the separation of paraplasm and spongio- 

 plasm other than our ability to recognize the nature and 

 purpose of the latter and our inability to do so with 

 regard to the former. 



The second essential structure of the cell is the nucleus. 

 In its most highly developed form this is a highly com- 

 plex organ. It appears as a spheroidal protoplasmic 

 body whose size bears a fairly constant relation to the 

 size of the cell though the proportion differs greatly in 

 cells of different kinds. It is usually enclosed in a hya- 

 line membrane, known as the nuclear membrane, and 

 consists of substance divisible into a part that is struc- 

 tureless and probably fluid, known as the nuclear juice, 

 or karyoplasm, and material that is for the most part 

 filamentous and known as the nuclear substance or 

 karyomitome. Staining reagents show that the struc- 



