CHAPTER XXIII 



Preservation of Fungus Colonies 



1. REASONS FOR PRESERVATION 



Tl I E span of time during which a fungus in culture is at prime varies 

 somewhat with the species. In most cases it is short. Thus most patho- 

 genic growths require two or three or more weeks to attain maturity and 

 may be at their best for only a week or 10 days. In order to keep a display 

 ot hmgi in culture and also to give our students a representative collection 

 of typical pathogens, we evolved a practical method by which a fungus 

 colony may be preserved in its typical form for an indefinite period. The 

 gross appearance of the colony remains unchanged for many months. Under 

 filtered ultraviolet rays, however, the color becomes noncharacteristic and 

 dull as soon as the growth is killed. This procedure eliminates all danger 

 of accidental human inoculation, an important consideration with virulent 

 fungi such as C. immitis. 



2. METHOD OF PRESERVATION 



The fungus is inoculated on a medium which has dried out somewhat, 

 as excessive moisture prevents the development of a radial colony. When 

 the colony has acquired a characteristic appearance, the cotton pledget is 

 moistened with 10 drops of a 40 per cent solution of formaldehyde and 

 replaced in the test tube. After 24 hours the pledget is trimmed off even 

 with the test tube and dipped in paraffin to make a completely air-tight 

 seal. This latter precaution is necessary to prevent evaporation of moisture 

 from the agar, with resultant shriveling of the fungus growth. 



BIBLIOGRAPHY 



l.i wis. ('.. \l.. wi) Hopper, \1. E.: Preservation of Fungus colonies 1>\ formaldehyde, Arch. 

 Dermat. & Sxph. 34:686, 1936. 



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