i LIVING MATTEE . 19 



Lastly, it should be noted that the unicellular animals which 

 have no membranes, such as amoebae, leucocytes, infusoria, and 

 other cells, often contain food-stuffs or other solid bodies which 

 they have ingested, e.g. diatoms, small algae, bacteria, etc. 

 (Metschnikoff), which are gradually digested, and appear as solid 

 inclusions in the protoplasm (see Fig. 1). 



IV. Many of the peculiarities which we have noted in the 

 constitution or structure of the cytoplasm are characteristic of the 

 nucleus also. This is usually a vesicular body, surrounded by a 

 membrane ; at other times it may assume various forms, and may 

 lose the enveloping membrane which divides it from the cytoplasm. 



Under a high magnification Biitschli detected an alveolar 

 structure similar to that of the cytoplasm, which presents the 

 appearance of a reticulum. The vesicles contain the nuclear fluid ; 

 the substance which forms them is termed a-chromatic, since it 

 does not stain with carmine, haematoxylin, or other dyes. Another 

 substance, peculiar to the nucleus, which does stain with dyes, and 

 is termed chromatic, can also be distinguished. This appears in 

 the form of small granules or filaments, threads diffused at the 

 nodal points of the a-chromatic substance, or collected in a heap 

 or kind of central skein (see Fig. 6). 



V. Chemical analysis of animal and vegetable organisms has 

 shown that the elements which enter most constantly and 

 abundantly into the composition of the cell are : 



Name. Symbol. Atomic Weight. 



Carbon C 12 -00 



Nitrogen N 14-04 



Sulphur S 32-07 



Hydrogen . . H TOO 



Oxygen O 16-00 



Phosphorus P 31-00 



Chlorine Cl 35-46 



Potassium K 39-14 



Sodium Na 23'04 



Magnesium Mg 24-00 



Calcium Ca 40-00 



Iron Fe 56 '00 



In addition to these twelve principal elements, other elements 

 occur, but in relatively smaller quantities ; they are not present 

 in every cell, but only in certain special plants and animals. 

 These are : 



Name. Symbol. Atomic Weight. 



Silicon Si 28-19 



Fluorine . . . . . F 18-98 



Bromine . . . . Br 79 76 



Iodine I 126-55 



Aluminium Al 27'00 



Manganese ..... Mn 53-90 



Lithium ..." Li 7'00 



