ISOLATION OF PATHOGENIC FUNGI 57 



large amount of mycelium. Often oxygen is the limiting factor for 

 growth and the greatest yield is obtained if the molds are grown in 

 a thin layer (about 1 cm. deep) of liquid medium. Flasks take too 

 much incubator space. We have in our laboratories used 1-liter, flat- 

 sided, narrow-mouthed prescription bottles which contain about 100 

 ml. each of medium. After inoculation, these are placed on their 

 sides and incubated so that the liquid is spread in a broad thin layer. 

 Narrow-mouthed bottles are essential to prevent air contamination. 

 When sufficient growth has occurred, the mycelium may be removed 

 by pulling the mat through the mouth of the tube with a hooked 

 wire, and the excess medium may be removed by straining through 

 gauze or sieve. In our laboratories large amounts of growth for ex- 

 tracting antigens and also for feeding to rats on diets have thus been 

 obtained. In industry special apparatus is used for mass production. 



Media for Biochemical Studies. In general, one studies the enzyme 

 actions of molds in the same manner as with bacteria, and such media 

 as gelatin, litmus milk, coagulated egg, or blood serum are useful. 

 Sugar fermentations are not important in the identification of molds 

 or actinomycetes, but they are of great importance in identifying 

 yeasts. INIethods for studying sugar fermentations by yeasts will 

 be discussed later. It is frequently desirable to determine the ability 

 of molds and actinomycetes to hydrolyze starch and cellulose. The 

 former may be determined by growing the organism in Petri dishes 

 on agar in which starch has been incorporated. After growth has 

 taken place the agar is flooded with diluted Lugol solution, which 

 will stain the starch blue but will leave a clear zone about the mold 

 if it has a diastatic action. The action on cellulose may be observed 

 by growing the organism in a medium containing various nutrient 

 salts, an inorganic source of nitrogen, but no source of carbon save 

 strips of filter paper. If the mold can digest cellulose, the paper 

 will be softened and eventually dissolved. 



Isolation of Pathogenic Fungi. In making cultures from derma- 

 tophytosis of the scalp the infected short hair stubs can be collected 

 by means of forceps and placed directly on the surface of Sabouraud's 

 agar slants or, better, placed first in empty sterile Petri dishes for 

 sorting and selection of suitable portions. If long hairs are taken the 

 infected basal portion should be cut off with sterile scissors or scalpel 

 and only this part planted. Two to four plants can be made on one 

 agar slant. 



In making cultures from dermatophytosis of the skin the lesion 

 should be first cleaned wdth a gauze sponge and 70 per cent alcohol. 

 Care should be taken to avoid lesions recently treated with a fungi- 



