20 Biological Stains 



the time the United States entered the second World War, this 

 proved a development of considerable significance. 



4. It has been realized for some time that the specifications 

 would be more satisfactory if they could eliminate statements that 

 the dye under consideration should be satisfactory for such and 

 such procedures. This has proved difficult because of lack of cor- 

 relation between chemical and optical characteristics, on the one 

 hand, and performance on the other. Of recent years apprecia- 

 tion has been growing of the fact that this lack of correlation 

 might be due to insufficient data; and that the only way to find 

 out would be to collect the data. Accordingly the assay labora- 

 tory of the Stain Commission has been going over its collection of 

 stain samples, some satisfactory and some unsatisfactory, to see if 

 any agreement between the two types of specification can be found. 

 It proves that such agreement is lacking in so many cases that 

 specifications based on performance must still be included; but the 

 data that are being collected are nevertheless proving distinctlj'' 

 valuable. They are showing better than ever before just what 

 limits of variation in chemical and physical specifications are per- 

 missible; and as a result it is now possible to establish better defi- 

 nitions of and specifications for biological stains than ever before. 

 Much of this new information is being incorporated into this edi- 

 tion of Biological Stains. 



Standardization Procedures now in Operation. This inter- 

 relation between the National Formulary specifications and the 

 standardization methods of the Stain Commission makes these 

 methods of considerable interest. It must be explained that the 

 standardization procedures adopted by the Stain Commission 

 have been entirely on the batch basis — that is, approval is not 

 given to the entire product of any one company, but is extended 

 to each individual batch that is put on the market. The reason 

 for this is that the Commission has never felt willing to place re- 

 liance on chemical or optical tests. All the specifications that 

 have been drawn up by the Stain Commission or by the National 

 Formulary Committee have contained statements which mean 

 essentially as follows: "The sample must prove satisfactory when 



tested by the following procedures: ". It is obvious that 



until it is known just how the results obtained in practical use 

 correlate with chemical or optical properties, any tests depending 

 upon performance must be carried out for each individual batch. 



Commission Certified stains are- now coming to be designated 

 with the initials "C.C." following the name of the dye. 



There is no need of listing here the tests actually employed by 

 the Commission; they are given in an appendix of this book where 

 they can be consulted by anyone who is interested. It must, 

 however, be explained that these tests fall into two groups : chemi- 

 cal and optical on the one hand; tests for performance on the other. 



