CULTIVATION AND EXAMINATION 39 



procedures, some of which have been developed for special tests, or for indi- 

 vidual mold problems. Practices useful in bacteriology are often applicable 

 to the problems of the mycologist. Selection of a procedure which satis- 

 factorily provides the information necessary to describe an Aspergillus calls 

 for discussion of a series of procedures commonly in use. Only in that way 

 may we show why some of these are adapted to the problems of identifying 

 an Aspergillus while others fail, for specified reasons, to furnish important 

 observations. 



Spot Inoculations 



Over long periods and in the hands of many investigators some type of 

 mass conidial inoculum has given dependable and reproducible results. The 

 most common method of transfer and, on the whole, probably the most 

 satisfactory one for maintaining a strain of Aspergillus, as well as other 

 molds, is the removal from the stock culture of a variable mass of conidia, 

 fruiting structures, or vegetative hyphae with some sort of needle or loop 

 and the transfer of this material to selected positions on fresh medium. 

 Practices differ. With the Aspergilli, colonies so placed as to permit radiate 

 development from the point of inoculation are most satisfactory for study. 

 Where there are two or three colonies to the plate, these eventually reach 

 into each other's zones of influence. They may blend and become indis- 

 tinct, or inhibit each other and leave sterile bands between the colonies. 

 Both types of culture furnish useful data. Usually, the line where two 

 colonies approach and partially or completely inhibit each other hastens 

 fruiting in the adjacent margins and permits favorable examination with the 

 compound microscope. The opposite margin of the same colony, unaf- 

 fected by competition, furnishes at the same time the normal and symmetri- 

 cal growth which is typical of the species. The one-colony plate usually 

 provides the most striking exhibit of the species, but the 2- or 3-colony plate 

 is the most generally useful (fig. 10). 



Once an Aspergillus has been obtained in pure culture, the most effective 

 way to insure that plates will contain 1, 2, or 3 colonies, as desired, is to 

 suspend a quantity of spores in melted agar at approximately 45° C, allow 

 this to solidify, and then transfer small quantities of the gelled suspension 

 to the surface of plates or agar tubes in the positions where the colonies are 

 desired. With the Aspergilli, as with all of the molds which produce dry 

 spores, it is often very difficult to secure placement of colonies at selected 

 positions, and only at such positions, without the use of some type of 

 wetted inoculum. 



In the routine examination of Aspergilli, where it is not essential that the 

 number of colonies be limited to 3 or less, satisfactory transfers have been 

 made by using a sharp nichrome wire as an inoculating needle and selecting 



