CHAPTER XXVI 

 FIXING AND STAINING MICROSCOPIC OBJECTS 



Ends in View. — Biological objects may be fixed, sectioned, 

 and stained either (a) to show structures built of cells, 

 as in morphological and embryological studies, or (6) to 

 show fine details of nuclear or cytoplasmic structures. 

 The methods for the first have been well worked out, and 

 are given in excellent manuals, such as Bolles Lee's Vade- 

 mecum. Here we shall only deal with certain methods for 

 ultimate fixing and staining of details of nuclear structures, 

 mainly in plant cells. 



Paraffin Sections. — In making paraffin sections of 

 anthers, the best method for details of plant chromosomes 

 seems to be to soak the anthers for three minutes in Car- 

 noy's alcohol-acetic-chloroform, before putting them in 

 another fixing solution, such as chrom-acetic-formalin 

 (Maeda). They may then be passed through graded 

 alcohols, without previously washing in water; imbedded, 

 sectioned, and washed well in 70 per cent alcohol, before 

 staining with haematoxylin or brazilin in 70 per cent 

 alcohol, being mordanted and differentiated by iron-alum 

 in 70 per cent alcohol; there being no soaking in water or 

 watery solutions. 



In ordinary paraffin sections of anthers of Aloe or Lilium, 

 the fixing will have occurred too slowly to show the chro- 

 momeres distinctly, or at all. It is well known that, even 

 in sections of root tips, only the outer cells may show 

 optimum fixation, it being sometimes hours before the inner 

 cells are fixed. Since the anther has, in many plants, a less 

 penetrable outer wall than the rootlet, the fixation of the 

 pollen mother cells is slow; so that there is time for inter- 

 mortem and post-mortem changes. 



With rapid fixing, the chromomeres are visible in the 

 leptotene, zygotene, and pachytene threads of Lilium, to 



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