50 A MANUAL OF THE ASPERGILLI 



serving large culture collections. It possesses certain marked advan- 

 tages : 



(1) There is no possibility of contaminants entering the sealed prepara- 

 tions. 



(2) The investigator recultivating the molds starts with the actual spores 

 contained in the original suspension. 



(3) The space required for storage of a large number of lyophile prepa- 

 rations is much less than for any other type of culture (fig. 13 B). 



Preservation in Soil 



Soil has been successfully employed as a means of preserving vigorous 

 stock cultures over long periods. As early as 1918, Barthel (Cent. Bakt. 

 II, 48: 340-49. 1918) reported the successful maintenance of yeasts and 

 bacteria in this medium and modifications of this technique are now em- 

 ployed in many laboratories for preserving bacteria. Greene and Fred in 

 1934 compared cultures of various molds preserved for two years in soil 

 with the same strains continuously maintained on malt extract and malt 

 extract-potato-glucose agars and on bread. In their experience, soil prepa- 

 rations were most satisfactory, and Professor Elizabeth McCoy (personal 

 communication) has recently reported cultures of A. sydowi preserved in 

 this manner to be viable after nine years. Since the publication of Greene 

 and Fred's work, the soil method has been rather generally used by the 

 Wisconsin group as a means of preserving valuable stock strains of molds. 

 Furthermore, it is known to have been successfully employed during the 

 past two years by a number of laboratories to maintain cultures of penicillin- 

 producing molds in a high and uniform state of productivity. The soil 

 substrate used by Greene and Fred was prepared as follows: 



"To air-dried orchard loam soil (Miami silt loam) sufficient water is added to 

 bring it to a moisture content of about 20 percent. The soil is then transferred in 

 convenient amounts (about 5 grams on a dry basis) to ordinary half-inch (1.27 cm.) 

 culture tubes. The tubes are plugged with cotton and given four 3-hour steriliza- 

 tions at 15 pounds per square inch (1 kg. per sq. cm.) pressure on alternate days, and 

 tested for sterility by addition of yeast-water-glucose broth to tubes selected at 

 random. The tubes are then inoculated with 1 cc. of a heavy spore or mycelium 

 suspension of the desired mold and kept at room temperature. That there is appre- 

 ciable growth and sporulation on the soil can usually be ascertained without difficulty 

 by direct microscopic observation. While the addition of nutrient to the soil may 

 bring about somewhat greater growth, it does not seem to enhance the keeping quali- 

 ties of the cultures. 



"It has been found possible to preserve on soil mold stocks used for large-scale 

 growth— namely, Aspergillus fischeri, A. sijdowi, and Penicillium chrysogenum— for 

 over 2 years without loss of their essential and desirable characters. . . . Moreover, 

 the gross colony characters have remained much more constant than did those of the 

 corresponding cultures maintained in the usual way on agar slants. The soil cultures 



