ANTAGONISM 283 



quickly became alkaline, and good growth could again be pro- 

 moted by the addition of acid. 



From similar studies with Aspergillus niger, Botrytis cinerea, 

 Cladosporhim herbarum, Fusarium solani, Mucor mncedo, Peni- 

 cillium glaucwn, and Rhizopus nigricans Lutz (1909) concluded 

 that a variety of materials cause staling. Although he was unable 

 to indentify any of them, he determined that some filtrates were 

 free from growth-inhibiting substances after passage through a 

 porcelain filter, whereas in others the staling products passed read- 

 ily through such filters. In some instances, moreover, heating to 

 80° C destroyed the inhibitory properties, indicating a relation- 

 ship to enzymes. Even after dilution with 20 volumes of water 

 the filtrates still greatly inhibited growth. 



Boyle (1924) grew Botrytis cinerea and Fusarium sp., isolated 

 from apple, on Richards' solution, potato extract, and apple ex- 

 tract. On each medium these organisms caused increased alka- 

 linity, which if eliminated in slightly stale media by addition of 

 acid, caused growth to be restored. At a later stage of staling, 

 however, adjustment of reaction did not correct conditions. He 

 concluded from these results that change in reaction is not per se 

 the limiting factor but that it accompanies the accumulation of 

 other inhibitory metabolic products. Filtration through a col- 

 lodion membrane removed part of the inhibitory properties. 

 Boiling of the staled medium also resulted in improved growth 

 but indicated that both thermolabile and thermostable products 

 were present. 



Pratt (1924, 1924a), using a species of Fusarium that rapidly 

 staled Richards' solution and Botrytis cinerea, which had little 

 staling properties, noted that hydrogen peroxide added to the 

 staled medium removes staleness, as does charcoal also, provided 

 that the alkalinity is first removed. Her chemical tests of media 

 staled by Fusarium indicate that ammonia, alcohol, and salts of 

 acetic, propionic, butyric, valeric, and lactic acids are produced. 

 Her general conclusion is that alkaline staling is caused by the pro- 

 duction of bicarbonates from the carbon dioxide of respiration 

 whenever basic radicals are set free. 



From the foregoing accounts it is clear that a variety of inhibi- 

 tory staling products are elaborated and that different species of 

 fungi may produce different products. Some of them may be 

 either simple or complex, some either heat-labile or heat-stable, 



