CHAPTER I 

 USES AND STANDARDIZATION OF BIOLOGICAL STAINS 



WHAT ARE STAINS? 



A QUESTION frequently asked is, "what are biological stains 

 and how do they differ from dyes?" The answer is simply 

 that they are dyes, but are adapted for very special purposes. 

 The manufacturer thinks of two classes of dyes, those intended for 

 general purposes and those specially adapted for biological use. 

 To him the "biologicals" are a class in themselves, notable chiefly 

 because of the care with which they must be manufactured and 

 the necessity of having them agree with rigid specifications so that 

 they will be satisfactory for the delicate procedures in which they 

 are employed. To the biologist, however, there are several classes 

 of products included among the "biologicals" and not all of them 

 are stains; there are medicinal dyes, bacteriostatic agents, and in- 

 dicators, which are not truly stains but are put in the same group 

 by the manufacturer. Strictly speaking, however, a biological 

 stain is a dye used for making microscopic objects more clearly 

 visible than they would be unstained. Such a dye may also serve 

 for textile purposes as well; but usually a special grade is needed 

 for biological use. The same statement is equally true (perhaps 

 more so) of medicinals and indicators; and since chemically they 

 are all very similar they are all considered in this book. Chief 

 stress, however, is laid on those which are employed primarily as 

 stains. 



THE HISTORY OF STAINING 



Considering how dependent microscopists are today upon the 

 use of stains, it is hard to realize that much important work had 

 been done with the microscope before the use of stains was at- 

 tempted. Although natural dyes such as carmine and indigo 

 were well known in the early days of the microscope, their use in 

 staining microscopic preparations does not seem to have become 

 common till about 1850; and anilin dyes were not put on the 

 market until 1856. Yet anyone who has studied the history of 

 biology must realize that many discoveries had been made with 

 the microscope before this period. 



It is safe to say, nevertheless, that the use of stains revolu- 

 tionized microscopic technic. The early microscopists were able 

 to make much progress without stains because of their painstaking 

 diligence. The work without stains must have been extremely 

 difficult, and it is hard on reading some of the old publications to 

 believe that some of the minute structures described were actually 

 seen. Few users of the microscope today would be likely to have 

 either the patience or the eyesight to do the work described in 



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