76 V. H. YOUNG 



tracted from the tubers of Helianthus tuberosus, "inulase." He 

 was able to demonstrate that the enzyme was not present in the 

 dormant tubers in an active condition but rather in the form of 

 its zymogen. Inulase has been very Uttle studied from the 

 point of view of the factors influencing its secretion although, as 

 will be seen below, some work of a valuable nature along this 

 line has been done. 



a. Literature of enzyme regulation 



It is a definitely established fact that environmental factors 

 are more or less efficient in stimulating or retarding the forma- 

 tion of enzymes in the fungi. In the literature this has been 

 termed "quantitative" regulation of enzyme formation. Many 

 have asserted that a change in environment does not cause a 

 change in the kind of enzyme produced, while others have as- 

 serted that this is not the case. A change in the environment in- 

 hibiting the formation of an enzyme, which would otherwise be 

 produced or a change initiating the formation of an enzyme not 

 usually produced, is termed "qualitative" enzyme regulation. 

 The study of enzyme regulation obviously centers around these 

 two ideas. Various environmental factors might be considered 

 as affecting enzyme formation: e.g., temperature, light, moisture, 

 the presence of oxygen, the presence of inorganic salts, and or- 

 ganic food substances. As a matter of fact the last of these 

 factors, i.e., organic food materials, has been the only one con- 

 sidered to any great extent, although some of the other factors 

 mentioned have been studied. 



Katz (1898) has studied the regulatory secretion of amylase in 

 Aspergillus niger, Penicillium glaucum, and Bacillus megatherium 

 and finds that the effect of various other substances serving to- 

 gether with starch as a source of carbon is in general to very 

 greatly inhibit the secretion of amylase. Cane sugar, grape 

 sugar, lactose, maltose, glycerin, quinic acid, and tartaric acid 

 were used. The rate at which starch disappeared from the culture 

 medium is taken generally as an index of amylase formation but 

 in certain cases the enzyme content of the mycelium is deter- 

 mined. With Penicillium glaucum, Katz finds that the presence 



