STAINING. 153 
What guoraanes are used with the aniline dyes and how are they 
used ? 
Aniline oil and also carbolic acid. The former is used in a satur- 
ated watery solution, to which the stock solution is added almost to the 
point of saturation. The latter is used in a weak, watery solution. 
In what way are the aniline dyes used with caustic potash to give 
a clear staining ? 
Methylin blue is the usual dye and may be used according to Koch’s 
formula, viz. : 
K Concentrated alcoholic solution methylin 
DlUG acess ss cticiusaidectinnmtanceecsgecsoeos ten 1 cc, 
“Vistilled Water.......cssssessceeseeseresseseensesess 200 cc. 
-0 per cent. solution liquor potassa............... 0.2 ce 
or according to Léfier’s formula, viz.: 
R Concentrated alcoholic solution of methylin 
WIG sisisniciis is can cae tires a duets stos sievioeaiue noes s 30 ce. 
Liquor potassa (1 to 10,000 or 0.01 per cent.).... 100 ce. 
™m 
The latter is the solution usually used. 
What is sometimes used as a bleaching or decolorizing agent ? 
Nitric acid, either in watery or alcoholic solutions. 
How are specimens of bacteria prepared upon cover glasses ? 
If the specimen to be examined is in a fluid state, first put a drop of 
distilled water on one side of a clean cover glass, and with a platinum 
wire, just sterilized, take a drop of the specimen and mix thoroughly 
with the water. Spread the mixture out into an even, thin’ layer and 
dry carefully without exposing it to too much heat. To fix the speci- 
men to the cover glass, pass the glass (held in a pair of forceps) 
through the flame of an alcohol lamp or Bunsen burner. It should be 
held specimen side up and passed back and forth three times about as 
fast as the pendulum of an old-fashioned clock swings. If the speci- 
men to be examined is semi-solid, a small piece is pressed into a thin 
layer between two cover glasses, these are then slid and not pulled 
apart, with the result of leaving the specimen spread out in a thin 
smear on each cover glass. This is dried and passed through the 
flame as above. 
How are these cover-glass specimens stained ? 
They may either be allowed to float, specimen side down, upon the 
solution of the dye (which solution may be either hot or cold, as 
