304 THE ANIMAL CELL. 



globulin which are present do not represent integral constituents of 

 the living protoplasm, but are merely to be regarded as food-stuffs, 

 or possibly even as decomposition-products of the protoplasmic 

 molecule. 



The proteids which are here found principally belong to the 

 nucleo-albumins, and it is to be noted that, in contradistinction to 

 those which occur in the nucleus, these nucleo-albumins contain 

 relatively but little phosphorus. The albuminous radicle in one of 

 them at least is quite constantly a vitellin. Glucoproteids may also 

 be present, but are not so constant as the nucleo-albumins. 



Of other constituents of the protoplasm, lecithin is the most 

 constant. In addition we find certain protagons, glycogen, choles- 

 terins, and in dead cells also paralactic acid, to which the acid 

 reaction of dead protoplasm is due. 



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 instances indeed almost the entire cell 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 

 w r ith 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 meslnvork 

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

 nucleoli possess a marked affinity for anil in 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 the nucleins 

 and the nucleo-albumins. The nucleins indeed are thought to con- 

 stitute the greater portion of the chromatic constituents of the 

 nucleus, and among them the so-called plastin apparently occupies 



