THE STRUCTURE OF CELLS 13 



of important changes in the protoplasm, are not necessarily 

 permanent organs of the cell. And a wide survey of the processes 

 of mitosis in the lower animals and plants serves fully to confirm 

 thiy conclusion. 



The Structure of the Resting Nucleus. 



It has already been said that it was not until the year 1875 

 that the nucleus was fully and universally recognised as an all- 

 important cell organ. Even as late as the previous year, Auerbach 

 published a treatise on its behaviour during cell-division maintaining 

 that it completely disappeared during the process, and he gave the 

 name of Karyolysis to the phenomenon in question. With the 

 recognition of the complex series of changes undergone by the 

 nucleus during division, and its obvious importance, in connection 

 with fertilisation, also discovered in 1875, it speedily formed an 

 object of serious study. And the investigations were not only 

 carried on in killed cells, but its behaviour during life, as well as 

 its chemical structure, presented attractive problems for solution. 

 The general outcome of these investigations is as follows : The 

 nucleus is delimited from the cell protoplasm (the cytoplasm of 

 Van Bambeke) by a membrane which was regarded by Schwartz as 

 consisting of a substance called by him Amphipyrenin. In some 

 cases, however, it appears not improbable that the membrane is at 

 least partly produced from the cytoplasm, as a kind of precipitation 

 membrane, whilst in other cases, as for example in some of the 

 coccidia, Schaudinn has shown grounds for thinking that the so-called 

 chromatin of the nucleus itself may contribute to its formation. 



Within the membrane the nuclear contents may be distinguished 

 as a matrix of a substance which stains with some difficulty, and 

 which forms a sort of meshwork within it. This is. the Linin of 

 Schwartz, and seems to closely correspond with the plastin, 

 distinguished chemically by Zacharias. In addition to the linin 

 there exists a more fluid gelatinous substance, the Paralinin of 

 Schwartz. Imbedded in the linin are a large number of granules 

 which, by reason of their exhibiting a strong affinity for certain 

 dyes, were termed Chromatin by Flemming. The chromatin consists 

 of a highly complex nitrogenous substance, and always contains 

 phosphorus. Chemically it belongs to the class of proteid 

 compounds classed as nucleins, and by analysis can be made to 

 yield proteids and nucleic acid. In addition to the true nuclein 

 chromatin, there have been described other inclusions within the 

 linin known as Lanthanin (Heidenhain) or oxy- or basi-chromatin 

 bodies, which appear to be related to the nuclein series, and which 

 perhaps are complex, high-graded substances which can be built still 

 further up to true nucleins. 



Most nuclei contain, besides these constituents, one or more 



