68 STUDYING MOLDS, YEASTS, AND ACTINOMYCETES 



acteristic clusters of blastospores and few to many large spherical 

 chlamydospores. However, strains which have been kept in culture 

 for long periods are not always typical in appearance, and fermenta- 

 tion reactions must be studied for identification. 



For finer details of morphology it is necessary to prepare slides. 

 Two stiff sharp Nichrome or steel needles are required. A bit of the 

 aerial mycelium is removed with a single thrust of one needle held 

 nearly parallel to the surface of the agar. The mycelium thus re- 

 moved should be touched momentarily to a small drop of 95 per cent 

 alcohol which has been previously placed on a slide, then removed 

 quickly to a drop of 10 per cent sodium hydroxide also previously 

 placed on the slide. It should then be carefully teased apart with 

 two needles and covered with a cover slip. A thin film left on the 

 slide by the rubbing of a finger across it just before the drops of 

 alcohol and sodium hydroxide are deposited will usually prevent the 

 spreading of the former and will facilitate the transfer of the material 

 from one fluid to the other. The alcohol wets the mycelium which 

 otherwise may be nearly opaque owing to the inclusion of air. The 

 sodium hydroxide is a better mounting fluid than -water because it 

 swells the hyphal walls, making certain morphological details more 

 apparent, and the preparation lasts longer. If the preparation is thin 

 the sodium hydroxide crystallizes around the edge, thus sealing the 

 cover and preventing dehydration for several hours. One may thus 

 determine with certainty the presence or absence of septa in the 

 mycelium, the structure of the sporophores and spores, the presence 

 or absence of chlamydospores, and the like. 



Instead of water some workers may prefer as a mounting fluid 

 Amann's medium, which has the following composition. 



Phenol, crystals 20 grams 



Lactic acid, syrup 20 grams 



Glycerol 40 grams 



Water 20 ml. 



These are dissolved together with gentle warming; then the follow- 

 ing is added. 



Cotton blue 0.05 gram 



This is the formula given by Linder,-^ save that the amount of dye 

 is greatly reduced. It serves as a combined fixing agent, stain, and 

 mounting fluid. The mycelium and spores will be stained blue; thus 

 much of the dye from the solution will be removed. Such a prepara- 

 tion, however, shows all the parts disarranged and is not permanent. 

 Permanent preparations showing the complete structure of the thallus 



