FUNGI AS TEST ORGANISMS 221 



indicate that the spore-inhibiting substance was either volatile or 

 unstable. This inhibitory substance was not identified. 



Fig. 45. Test for antibiotic production by growing two organisms in association on 

 the same agar plate. Helminthosporium sativum on the left and an unidentified 

 actinomycete on the right. 



TESTING FABRIC PROTECTANTS 



While the deterioration of cellulosic materials exposed to the weather 

 or in contact with the soil is not solely due to the action of bacteria and 

 fungi, these organisms are the chief agents of destruction. The problem 

 of deterioration of cellulosic materials has received a vast amount of 

 attention, especially in connection with military materiel in humid tropic 

 climates. Work on this problem involves the identification of the respon- 

 sible microorganisms, laboratory tests, and use of test fungi in evaluating 

 protectants. 



The basis of the various methods for determining cellulolytic activity 

 consists in inoculating cotton duck or other test material with the fungi 

 under test. The degree of cellulolytic activity is determined by measur- 

 ing the decrease in tensile strength of the test specimen. The test 

 medium used is usually an inorganic salt solution having pH 6.8. It is 

 desirable to use a buffered medium inasmuch as cellulase is most active 

 around pH 7. White et at. (1948) note that many fungi which are 

 strongly cellulolytic under laboratory conditions cause but httle damage 

 in the field. They believe that, under a given set of natural environ- 

 mental conditions, the actual decay of fibers is caused by a relatively 

 few species of fungi. Among the strongly cellulolytic fungi are Mem- 



