14 CULTURE METHODS AND TECHNIQUE 



followed by the potash solution or the cleaning mixture, as occasion 

 may demand. In either case the tubes are thoroughly rinsed ulti- 

 mately with distilled water, the outside of each wiped dry, and 

 they are then placed upon a test tube rack. In order that they may 

 dry rapidly and without blemish, they may be rinsed with 95 per 

 cent alcohol. A considerable quantity of alcohol may be used in 

 the first tube, the top of which when shaken is closed with the 

 finger. The same alcohol may thus be used for twenty or more 

 tubes successively. Tubes containing agar, or old cultures, are more 

 easily cleaned after being boiled for some time in the steam steril- 

 izer or in the autoclave. 



Petri dishes. These are generally cleaned with hot water and 

 soap. They should be thoroughly rinsed in clean, hot water and 

 wiped while yet hot. It is seldom necessary to leave cultures, or 

 the agar employed in cultures, in these dishes until the medium 

 becomes hard and dry. If so, it may be essential to soak or steam 

 the dishes a long time before cleaning. 



Flasks. It is difficult to get at the interior of flasks with any 

 type of brush, whereas reagents are readily employed in cleaning 

 such apparatus. The chromic acid mixture should then be employed, 

 and afterwards the flasks are rinsed and treated with alcohol as for 

 test tubes. If the flasks are desired for immediate use, after the 

 alcohol treatment, they should be rinsed with a small quantity of 

 ether, and may then be rapidly dried with a blast or foot bellows, 

 if one is convenient. 



Slides and cover glasses. When new, or when stained, these 

 may be effectively cleaned by the chromic acid mixture, in which 

 they should remain from twelve to twenty-four hours. They are 

 next rinsed, and the slides wiped directly, while the covers should 

 be wiped with cheese cloth or linen after a transfer to alcohol. 

 When the slides are soiled with paraffin, wax, vaseline, or other 

 oily material, boiling in the potash solution or in carbonate of soda 

 will be necessary. The same treatment should be used for tubes 

 sealed with paraffin. Balsam preparations are cleaned by soaking 

 for some time in 75-90 per cent alcohol, and then by rinsing in 

 waste xylol, benzine, or other such solvent of the balsam. 



Special methods. For studies in nutrition, germination experi- 

 ments with special stimuli, and other very careful physiological 



