CHAP, iv.] from 1838 to 1851. 323 



refraining from all speculative consideration of cases that lay 

 clearly before him, and his views were still undecided in 1845, 

 when Unger and Nageli had already made good observations 

 on the formation of tissue-cells in growing organs (' Vermischte 

 Schriften,' 1845, p. 336). 



Schleiden's theory of cell-formation arose out of a curious 

 mixing together of obscure observations and preconceived 

 opinions, and reminds us indeed strongly of the old notions of 

 Sprengel and Treviranus ; it is true that he distinctly rejected 

 their views, but he too made new cells arise from very minute 

 granules, and his theory like theirs did not rest on any thorough 

 course of observation. 



Robert Brown (see his Miscellaneous Writings, edited by 

 T. T. Bennett, I.) had discovered the nucleus in the cells 

 of the epidermis of Orchidaceous plants in 1831, and had 

 shown that it was very generally present in the tissue-cells of 

 Phanerogams, but had obtained no results from his discovery. 

 The cell-nucleus lay undisturbed, till Schleiden suddenly made 

 it the soul of his theory and the starting-point of all cell-form- 

 ation. He considered that the nucleus was formed from the 

 mucilaginous contents of the cell, which he assumed on insuf- 

 ficient grounds to be of the nature of gum ; this he called the 

 cytoblastem, and the nucleus itself the cytoblast. As he states 

 that his cytoblastem becomes yellow and granular in solutions 

 of iodine, we may recognise in it our own protoplasm. 



We make acquaintance with Schleiden's theory of cell-form- 

 ation in its original form, if we turn to his treatise, ' Beitrage 

 zur Phylogenesis ' (in the ' Archiv fur Anatomic, Physiologic, 

 etc.' von Johannes Miiller, 1838). The work begins with some 

 remarks on the general and fundamental laws of human reason, 

 etc., discusses the literature of cell-formation in a few lines 

 without mentioning von Mohl's numerous observations, goes 

 on to mention the general occurrence of the nucleus which here 

 receives its new name, then occupies itself with gum, sugar, 

 and starch, and at last comes to the main subject. There are 

 Y 2 



