4. The sample must prove satisfactory for use in the Endo medium. In making 

 this test the following technic should be used: A saturated alcoholic solution is 

 diluted 2 to 3 times, the dilution to be such that no precipitation occurs when mixed 

 with a sodium sulphite solution. Then add 0.5 cc. of the saturated and the diluted 

 fuchsin solutions each to 10 cc. of a 2.5 per cent sodium sulphite solution. Select 

 the strongest of these which shows no precipitate and add it to the other ingredients 

 of Endo agar, sterilize and cool. It should then be colorless, but the color must be 

 restored by the colon and dysentery organisms when inoculated upon it. The test 

 must be made by one familiar with the technic in question. 



5. It must be understood that as basic fuchsin is used in other special forms of 

 technic, new standards may be called for. The present specifications apply par- 

 ticularly to the above mentioned two uses: but samples fulfilling them are ordi- 

 narily satisfactory for all histological purposes. 



SPECIFICATIONS FOR ACID FUCHSIN 



1. Acid fuchsin designed for staining and indicator purposes must correspond 

 to Colour Index No. 692. Inasmuch as the dyes of this type on the market are 

 mixtures of greatly varying composition, and it has not yet been shown that any 

 one of the components of these mixtures is better for biological purposes than any 

 of the others, no definite physico-chemical specifications are made at the present 

 time, with the reservation that more specific requirements may be drawn up at a 

 later date if future work shows them to be desirable. 



2. Acid fuchsin samples to be certified by the Commission should be of such a 

 strength as to consume not less than 2.0 cubic centimeters of normal TiCls solution 

 per gram of sample. Such samples would have a total dye content of approximately 

 60 per cent. 



3. Acid fuchsin samples for certification should prove satisfactory counter- 

 stains in general histological work. They should in particular prove satisfactory 

 in the Bensley technic for staining mitochondria, and in the Mallory connective 

 tissue stain (with anilin blue and orange G). They should be tested for these 

 purposes by histologists skilled in the technic in question. 



4. The samples shall prove satisfactory for use in the Andrade indicator. For 

 this purpose they shall be tested as follows: Dissolve 0.2 gram in 100 cc. water, 

 neutralize by adding between 15 and 25 cc. of Normal NaOH. When neutralized 

 with the proper amount of the reagent, the solution should become a straw color 

 upon standing and should impart no noticeable color to ordinary bacteriological 

 nutrient agar when added at the rate of 1 per cent. The red color should be 

 restored in this medium by the colon organism when growing in the presence of 

 any sugar attacked by it. 



5. Labels to be used on the acid fuchsin samples should state the formula giving 

 best results with the sample in question in preparing the Andrade indicator. 



SPECIFICATIONS FOR GENTIAN AND CRYSTAL \^OLET 



1. Crystal violet samples shall contain no dye except hexa-meth\l pararosanilin 

 (Colour Index No. 681), having its absorption maximum at 590fifi when de- 

 termined in a cell of 1 milimeter thickness in a spectrophotometer. 



134 



