344 MARGARET R. LEWIS AND WARREN H. LEWIS 



dria and other granules. The nucleus ai:)])ears as a finely gran- 

 ular body surrounded by a definite nuclear wall with one or 

 more nucleoli. The nucleolus is never a round compact body, 

 but instead is a coarsely granular ragged body, often large in 

 proportion to the size of the nucleus. The nucleolus can read- 

 ily be seen with the low power even when the outline of the 

 nucleus cannot be distinguished. At one side of the nucleus 

 there is usually present the central body (idiozome). 



When permanent preparations were desu'ed the cover-slip was 

 removed from the vaseline ring and the entire culture fixed to 

 the cover-slip by means of osmic acid vapor. After fixation 

 the explanted piece was often torn ofi' from the cover-slip, leaving 

 the new growth, in order to facilitate certain staining processes. 

 Since the growth is very thin it was unnecessary to cut sections. 

 The cover-slip with the fixed growth was treated as one would 

 sections on a slide. 



FIXATION 



The entire process of fixation can be watched and studied 

 upon any cell, as, for example, one that has been under obser- 

 vation for some time. While the preparation is observed under 

 the microscope some of the fixing solution can be introduced 

 into the cavity of the slide through an opening made in the 

 vaseline ring, which seals the coverslip to the slide. The speci- 

 men can be fixed with either vapor or fluid. If a vapor is used, 

 as of osmic acid, a small drop of a 2 per cent solution of osmic 

 acid is introduced on the bottom of the cavity so that it does 

 not come in contact with the hanging drop. If a solution is 

 used, enough is introduced to fill the entire cavity and mix with 

 the hanging drop. 



The vapor from a freshly made 2 per cent osmic acid solu- 

 tion gave the best results, and when used with care resulted 

 in a fixed cell, which more closeh' resembled the living cell than 

 any other method we have used. The osmic acid vapour seems 

 to cause a precipitation of the cell structures in the form of 

 minute granules. Even after such fixed specimens are stained 

 by means of ii-on hematoxylin the general character of the cyto- 



