12 REPORT — 1900. 



nuclei in the blood corpuscles of the chick and the pig, which he regarded 

 as evidence of the production of new corpuscles by division of the 

 nucleus within a parent cell ; but it was not until some years afterwards 

 (1850 to 1855) that he recorded additional observations and recognised 

 that division of the nucleus was the starting-point for the multiplication 

 of cells in the ovum and in the tissues generally. Remak's view was that 

 the process of cell division began with the cleavage of the nucleolus, 

 followed by that of the nucleus, and that again by cleavage of the body 

 of the cell and of its membrane. Kolliker had previously, in 1843, de- 

 scribed the multiplication of nuclei in the ova of parasitic worms, and 

 drew the inference that in the formation of young cells within the egg 

 the nucleus underwent cleavage, and that each of its divisions entered 

 into the formation of a new cell. By these observations, and by others 

 subsequently made, it became obvious that the multiplication of animal 

 cells, either by division of the nucleus within the cell, or by the budding 

 off of a part of the protoplasm of the cell, was to be regarded as a widely 

 spread and probably a universal process, and that each new cell arose 

 from a parent cell. 



Pathological observers were, however, for the most part inclined to 

 consider free cell-formation in a blastema or exudation by an aggregation 

 of molecules, in accordance with the views of Henle, as a common pheno- 

 menon. This proposition was attacked with great energy by Virchow in 

 a series of memoirs published in his ' Archiv,' commencing in Vol. 1, 1847, 

 and finally received its death-blow in his published lectures on Cellular 

 Pathology, 1858. He maintained that in pathological structures there 

 was no Instance of cell development de novo ; where a cell existed, there 

 one must have been before. Cell-formation was a continuous develop- 

 meni, by descent, which he formulated in the expression omnis cellula 

 e celluld. 



Karyokinesis. 



Whilst the descent of cells from pre-existing cells by division of the 

 nucleus during the development of the egg, in the embryos of plants 

 and animals, and in adult vegetable and animal tissues, both in healthy 

 and diseased conditions, had now become generally recognised, the 

 mechanism of the process by which the cleavage of the nucleus took place 

 was for a long time unknown. The discovery had to be deferred until 

 the optician had been able to construct lenses of a higher penetrative 

 power, and the microscopist had learned the use of colouring agents 

 capable of dyeing the finest elements of the tissues. There was reason to 

 believe that in some cases a direct cleavage of the nucleus, to be followed 

 by a corresponding division of the cell into two parts, did occur. In the 

 period between 1870 and 1880 observations were made by Schneider, 

 Strasburger, Biitschli, Fol, van Beneden, and Flemming, which showed that 

 the division of the nucleus and the cell was due to a series of very remark- 

 able changes, now known as indirect nuclear and cell division, or karyo- 



