THE ANIMAL CELL. 321 



The total amount of solids, including the mineral salts, which are 

 thus found in protoplasm, is always small, and probably never 

 exceeds 15-20 per cent., while the remaining weight is referable to 

 water. In some cells almost the entire body is taken up by the 

 nucleus, and in the lymphocytes, for example, only 1.76 per cent, of 

 the total 79.21 per cent, of albumins, as calculated for the dry 

 material, is present in the protoplasm. 



The nucleus may be regarded as the essential living part of all 

 animal and vegetable cells, and from it, no doubt, the various func- 

 tions of the cell as a whole are directed. It is intimately connected 

 with the process of reproduction, and during this process it under- 

 goes a series of most remarkable changes, which are collectively 

 termed the karyokinesis or karyomitosis of the nucleus. Micro- 

 scopically the quiescent nucleus represents a round or oval little 

 body, which usually occupies an excentric position within the cell. 

 It is surrounded by a nuclear membrane, and contains a meshwork 

 of extremely fine fibrils, and one or more nucleoli. Both fibrils and 

 nucleoli possess a marked affinity for anilin dyes, while the nuclear 

 membrane and the more liquid hyaloplasm within the nuclear 

 meshes are scarcely stained at all. We therefore recognize in the 

 nucleus the existence of chromatic and achromatic substances, which 

 are usually spoken of as the nuclear chromatins and achromatins. 

 During the process of division a peculiar spindle-like body is also 

 observed in the nucleus, which, like the nuclear hyaloplasm, is 

 achromatic. 



In contradistinction to the cellular protoplasm, the nucleus con- 

 tains a much larger quantity of solids, but here as there the albu- 

 mins stand in the foreground. Whether or not native albumins 

 also occur in the nucleus is not definitely known, but it is 

 generally assumed that this is not the case. The proteids, on the 

 other hand, are abundant and largely represented by nucleopro- 

 teids. They are thought to constitute the greater portion of the chro- 

 matic constituents of the nucleus. Especially abundant is a nucleo- 

 proteid, which Kossel and Lilienfeld first obtained from the thymus 

 gland of the calf. This they termed nucleohiston, from the fact 

 that on treatment with hydrochloric acid it is supposedly decomposed 

 into a nuclein leuconuclein and histon. Bang, however, denies 

 that this nucleohiston is a true histon. He regards it as an albu- 

 minate, and states that he could not demonstrate a nucleinate of 

 histon in the leucocytes. 



Whether lecithins, protagon, and glycogen, which are constantly 

 found in the cellular protoplasm, likewise occur in the nucleus, is 

 not known. 



Of mineral constituents, iron is constantly present, and appar- 

 ently occurs in combination with the nucleins in organic form. 



Justus has further shown that every nucleus normally contains 

 iodine. 



