Uses and Standardization of Stains 21 



In interpreting results, greatest weight is given to the tests for 

 performance. It not infrequently happens that a batch of some 

 stain will prove to give perfectly satisfactory results in all the 

 latter, but proves slightly low in dye content, or disagrees in some 

 respect with optical characteristics called for in the specifications. 

 The rule in the case of such a sample is to approve it on the basis 

 of its performance in spite of the slight non-conformitv in the case 

 of chemical or optical characteristics. 



Batches of dyes thus approved by the Commission are sold by 

 the companies with a special label furnished by the Commission, 

 known as the certification label. This label indicates the certifica- 

 tion number of the batch and is not supposed to be employed for 

 any batch other than that on which it is issued. A certification label 

 on any bottle of stain means therefore, five things: (1) a sample of 

 the batch bearing the label has been submitted to the Commission 

 for testing and a portion of the sample is permanently on file; (2) 

 the sample proves true to type, as judged by spectrophotometric 

 tests; (3) its dye content is up to specification and is correctly in- 

 dicated on the label; (4) it has been tested by experts in the pro- 

 cedures named on the label and has been found satisfactory by 

 them; and lastly, (5) no other batch can be sold under the same 

 certification number except by such a flagrant breach of confidence 

 on the part of the company as to risk losing the good will of the 

 Commission. 



At the present time (1952), 51 stains have been put on the certi- 

 fication basis. These include all the most commonly used 

 biological stains as well as a few in which the Stain Commission 

 lias become interested, although they are not so extensively em- 

 ployed in the laboratory as most of the others on the list. 



There are, at the time this sixth edition goes to press, nine com- 

 panies in the United States and one in Canada submitting their 

 stains to the Commission for certification before putting them on 

 tlie market. It must be realized, however, that no one of these 

 concerns necessarily manufactures all the stains which it thus 

 submits; but in the case of any stain which is manufactured else- 

 where, the company takes responsibility for its performance as a 

 biological stain on the basis of tests made to show its adequacy, 

 and in many instances carries out a certain degree of purification 

 or other processing before putting the stain on the market. One 

 of these companies puts on the market every stain now on the 

 certification list. Three other companies submit samples of over 

 half the stains thus listed, while the other companies merely re- 

 quest certification of one or two dyes in which they specialize. 

 No dyes have yet been certified by the Stain Commission sub- 

 mitted by any concern outside North America. The reason for 

 this is because of the difficulty in handling the certification of 

 stains on the batch basis with a concern that is located at a dis- 



