32 ESSENTIALS OP BACTERIOLOGY. 



Iodine as used in Gram's Method. Belonging to this group, 

 but used more in the sense of a protective, is tr. iodine. It picks 

 out certain bacteria, which it coats ; prevents them from being 

 decolorized, but allows all else to be faded. Then by using one 

 of the acid or tissue dyes, a contrast color, or double staining is 

 obtained. Many of the more important bacteria are not acted 

 upon by the iodine, and it thus becomes a very useful means of 

 diagnosis. 



Formulas of different Staining Solutions. 



I. Saturated Alcoholic Solution. 



Place about 10 grammes of the powdered dye in a bottle and 

 add 40 grammes of alcohol. Shake well and allow to settle. 

 This can be used as the stock bottle. 



II. Weak Solutions. 



Made best by adding about 1 part of number I. or stock solu- 

 tion to 10 of distilled water. This is the ordinary solution in use. 



III. Aniline Oil Water. 



Aniline oil 5 parts. 



Distilled water . . . .100 parts. M. 

 Shake well and filter. To be made fresh each time. 



IV. Aniline Water Dyes. 

 Sat. alcoh. sol. of the dye . . 11 parts. 

 Aniline oil water . . . . 100 parts. 



Abs. alcohol 10 parts. M. 



Can be kept 10 days. 



V. Alkaline Methylin Blue. 



A. Ijb'ffler's. 



Sat. ale. sol. methylin blue . . 30 

 Sol. potass, hydrat. (1-10,000) . 100 M. 



B. Koch's. 



Sol. potass, hydrat. (10 per cent.) 0.2 

 Sat. ale. sol. methyl, blue . . 1.0 

 Distilled water 200.0 M. . 



