Aspergillus is a very common mold found on bread, cheese, and decayed and preserved fruit. In the conidial stage it is green and in the ascosporic stage yellow, reddish yellow, or reddish brown. Aspergillus is almost sure to appear upon bread which is kept moderately moist, because the conidia are usually abundant in the atmosphere. If the bread be wet with a 10 per cent solution of cane-sugar or with grape juice, this stage appears sooner and in greater abundance. A temperature of 22 to 30 C. is also a favorable condition.
The perithecial stage is not found so frequently, but can sometimes be secured by examining moldy preserves. The sexual stage has been induced. Soak a piece of bread in a 20 per cent solution of grape-sugar in grape juice; upon this sow the spores and keep at a temperature of about 28 C. After 4 or 5 days, begin to examine. A 40 per cent solution of cane-sugar in the juice of prunes is also a good nutrient solution.
For class use or for permanent preparations it is best to select rather young material which shows various stages in development, from the swollen end of the hypha to the ripe spore.
Fix in 1 per cent chromo-acetic acid (1 g. chromic acid and 1 c.c. acetic acid and 100 c.c. water) for 24 hours; wash in water 24 hours, stain sharply in eosin, transfer to 10 per cent glycerin, and follow the Venetian turpentine method.
Material may be fixed in corrosive sublimate-acetic acid (corrosive sublimate 2 g., glacial acetic acid 2 c.c., and water 100). Use it hot (85 C.). One minute is long enough. Wash in water and add, a few drops at a time, the iodine solution used in testing for starch. At first, the brownish color caused by the iodine will disappear, but after a certain amount has been added the brownish color will remain. Stain in eosin or iron-haematoxylin and follow the Venetian turpentine method.
A very rapid method for this and for similar small filamentous forms may be added. Forms as large as Thamnidium elegans can be mounted successfully by this method.
1. 100 per cent alcohol, 2 minutes. 2. Eosin (aqueous), 2 minutes. 3. 1 per cent acetic acid, 2 to 10 seconds. 4. Mount directly in 50 per cent glycerin and seal.
If the material gets through the first three stages without shrinking but collapses at the fourth, put it into 10 per cent glycerin and allow it to thicken, following the Venetian turpentine method.
The earlier perithecial stages are more instructive when mounted whole; but later stages, even before the formation of the asci, are very unsatisfactory by this method, and should be cut in paraffin.
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