I50 ANATOMY OF THE YEAST CELL. 



been taken up also by G. Hieronvmus (I.) and A. B. Macallum 

 (I.). On the other hand Schmitz's discovery was confirmed by 

 E. Chr. Haxsen (XVI.), A. Zalewski (I.), E. Zacharias (I.), 

 H. McELLER (IL), P. A. Dangeard (II.), Fr. a. Janssens (I.), 

 and L. Buscalioxi (I.). The first-named Danish worker also 

 stated that he had been able to discern the nuclei in the cells 

 of the films produced by Sarcharoniyres Padorianus I. and //., 

 and S. ellipsoideus I., in many cases without trouble. Moeller 

 also observed the nuclevis as a homogeneous, pale reddish disc, 

 and expresses the opinion that the same has been mistaken for 

 a vacuole by many observers. The present author is able to 

 confirm this from his own experience as a teacher, this mistake 

 regarding the cell nucleus being of somewhat frequent occm*- 

 rence among practitioners. 



The method tested by H. Mckller (III.), and recommended 

 by him as the best for rendering the nucleus visible, is a 

 staining process proposed by H, Heidexhain (I.) ; and Jaxssens 

 and Leblaxc (I.) also recommended the same as being the most 

 relial;)le. The method of application consists in fixing a cover- 

 glass streak-preparation with a solution of iodine in potassium 

 iodide, and hardening the same in alcohol as recommended by 

 McELLER (II.) ; then mordanting it in a 2^ per cent, solution of 

 iron alum, and finally staining with a h per cent, solution of 

 hsematoxylin. 



The morphological varialiility of the cell nucleus was already 

 recognised by Schmitz. In young cells the nucleus is globular, 

 but flattens with increasing age to a disc of sinuous contour 

 (Zalewski found this elliptical). The dimensions are consider- 

 able, the diameter in some instances attaining to one-third that 

 of the cell itself. According to the researches of Buscalioxi 

 and Casagraxdi (I.) with Saccharomyces guttulahis, the dimen- 

 sions of the nucleus vary with the size of the cells. Except in 

 the case of ascosporulation (to be referred to later on) Jaxssexs 

 and Leblaxc (I.) failed to find more than a single nucleus in 

 any yeast cell during their experiments with pure culture. 



The first observation in connection with the internal structure 

 of the yeast cell nucleus, namely the occurrence of a nucleolus, 

 was made by Zalewski (I.) in 1885. H. Mceller (II.) in 1892 

 questioned the accuracy of this report, but it was confirmed 

 a year later, almost simultaneously, by Daxgeard (II. ) and 

 Janssens (I.), and also later by H. Wager (I.), who found that 

 the cell nuclei of yeast exhibit both a membrane and a 

 nucleolus. The latter is of globular shape, is situated about 

 the centi'e of the nucleus, and measures in diameter up to one- 

 third that of this last named. The space between the membrane 

 and the nucleolus is filled with karyoplasm, which, according to 

 the researches of Janssens and Leblanc (confirmed liy H. Wager) 

 has a filamentous structure, forming a soi't of framework. The 



