The Microscope. 67 



For more than a century, cells were regarded as vesicles con- 

 taining a homogeneous liquid. But in 1781 Fontana discovered 

 the nucleus, which he illustrates with its nucleolus, and in his 

 second volume, he describes the nucleus as " an ovoid body, pro- 

 vided with a spot in its centre." Moreover, in various places he 

 speaks of the granular contents of the cells, and clearly repre- 

 sents by figures adipose cells with their numerous fat globules. 



About this time were also made the first experiments in micro- 

 chemistry, as stated by Baker. Fontana employed acids and 

 alkalies and even vegetable colors, and Meyen in 1828, enumer- 

 ates a series of bodies, such as starch, chlorophyll bodies, crys- 

 tals,'etc., as having been found in vegetable cells. The works of 

 Meyen are interesting as they give a summary of what has been 

 done in micro-chemistry during the past period. In 1831, R. 

 Brown greatly advanced the knowledge of the cell by confirm- 

 ing and extending considerably the researches and discoveries of 

 Fontana ; but his merit consists, not so much in having discov- 

 ered the nucleus, as in having recognized it as a normal element 

 of the cell. 



Almost at the same time, Mirbel, in his " Researches on the 

 Marchantia " (1831-32), mentions the nucleus and calls it 

 " spherule." Finally, the researches of Meyen, Schleiden, Unger, 

 Schwann and Nsegeli completely demonstrate that the nucleus 

 must be regarded as an essential element in the cell, and that it 

 may be found in the majority of both animal and vegetable cells. 

 Schleiden in 1838 calls the nucleus " cytoblast," and attributes 

 to it a special function in the formation of cells. Later on, 

 Martin Barry and John Goodsir contended that the reproduc- 

 tion and multiplication of cells were due to self-division of the 

 nucleus, and thus gave greater importance to the nucleus than 

 had previously been assigned to it. 



As early as 1781, Fontana, had mentioned the nucleolus, but 

 Valentine was the first to illustrate it by a figure in his " Reper- 

 torium." He speaks of the nucleolus as a small, round cor- 

 puscle, " a kind of second nucleus " in the interior of the nucleus. 



According to Schleiden, the nucleolus is a sort of kernel, 

 " kernchen," and Schwann, calls it " Kernkorperchen ; " finally, 

 in the same year, 1839, Valentine uses at the same time the 

 terms nucleolus, and " Kernkorperchen," and these two terms 

 are still in use. 



