STAINS AND STAINING. 288 



Nuclear Stains. 



As in both animal and vegetable sections it is generally the 

 nuclei which form the geographical landmarks of the structure, the 

 most important class of reagents which are used in any of the 

 branches of microscopical work, are the " nuclear stains." 



They are so called because they stain the nucleus more strongly 

 than the rest of the structure, and when certain precautions are 

 adopted the differentiation can be made so complete that the 

 nuclei will be strongly stained in an otherwise colourless section. 

 Some sections illustrating this will now be projected on the screen. 



There are several nuclear stains, the most important of which 

 is haematoxylin, and when a good solution is used the results 

 are excellent. 



Logwood and HcBmatoxylin. 



In the early history of microscopy, various preparations of 

 logwood were used, but these have been practically discarded in 

 favour of the more definite crystallised haematoxylin. The litera- 

 ture of this stain is very confusing and contradictory. Not only 

 do the various writers differ amongst themselves as to its merits 

 and demerits, but it liappens occasionally that curious contradic- 

 tions occur in the same book. 



In one of the best books on staining (published in 1890) 

 the chapter on haematoxylin contains the following remarks : — 



" None of the solutions are perfectly stable ; only one or two 

 are fairly so. In general, freshly prepared solutions stain badly 

 and diffusely ; they ought to be allowed to ripen before use. 

 This takes, according to the nature of the solution, a few hours, 

 or days, or months. On the other hand, kept solutions gener- 

 ally go bad by precipitating or becoming acid or becoming 

 mouldy. Most of the solutions, when in good staining order, 

 have a great tendency to overstain. The stain is fairly perma- 

 nent in balsam, but is sure to fade a little, and may fade a great 

 deal." 



This would be enough to prejudice any beginner against 

 hasmatoxylin, were it not that on the next page, under Dela- 

 field's solution, it is stated : — " The solution keeps well, it may 

 be said for years. It is extremely i)owerful, and when properly 

 used is very precise." A few pages further on in the same book 



