THE CELL. 11 



of microscopic size, contain only one nucleus. A similarity in the 

 form of the nucleus to that of the cell is not noticeable. In the 

 younger cells it is approximately spherical ; after the period of cell- 

 growth it becomes more ellipsoidal. It often lies near the cell-wall 

 imbedded in the plasm, sometimes it is suspended in the cell-lumen 

 by means of plasmic threads. To demonstrate the presence of the 

 nucleus it is advisable to kill the cell with concentrated picric acid, 

 which " fixes " the plasm, and subsequently to stain it red with 

 haematoxylin solution or green with methyl green. 



The nucleus, again, contains one or more nucleoli.' The nucleus 

 (exclusiue of nucleoli) contains besides true albuminous substances 

 a characteristic compound or group of compounds also albuminoid 

 in nature, namely, the phosphorus-bearing nuclein. It swells in a 

 10^ solution of NaCl and is dissolved in a solution of potassium 

 hydrate which distinguishes it from true albumen. 



As a rule the nucleus is located in that portion of the cell where 

 growth {growth in thickness or surface of cell-wall) is the most 

 active or where it continues the longest. Usually the nucleus assumes 

 a definite position only in the undeveloped cell, later the position is 

 indefinite. Rarely it may assume a definite position for a second 

 time. 



From the foregoing statements it is to be supposed that the 

 nucleus is of special significance in the processes of cell-growth. 

 What role it really does play and what functions it subsequently 

 subserves is still a question. The observations made by Klebs upon 

 artificially-divided cells are of special interest. It was observed that 

 only that portion of the cytoplasm which contained the nucleus is^ 

 capable of growing in length and surrounding itself with a mem- 

 brane, while the function of the remainder is assimilation only. 



The diflFerence between cell-division and free cell-formation is, 

 according to our present knowledge of nuclear behavior, not so 

 great as was formerly taught. During each cell-division and in 

 general during each free cell-formation there is a nuclear division. 

 The so-called indirect nuclear division occurs most frequently, and 

 is connected with extensive changes in the nuclear substance. The 

 details of this mode of nuclear division have been made known by 

 Stkasburgek, Flemming, Guignakd, and Heusee. 



I will not enter into a comprehensive description of indirect 



' There are often denser portions noticeable within the nucleoli. — Trans. 



