126 V. H. YOUNG 



As has been already suggested, studies of enzyme regulation 

 are grouped around the idea of either a qualitative or a quanti- 

 tative regulation. Early investigators who worked in this field 

 were prone to look for qualitative enzyme regulation in the fungi. 

 The great ease, with which various forms like Penicillium and 

 Aspergillus have been found to adapt themselves to growth on 

 almost any organic substance, suggests that these fungi must be 

 able to produce enzymes acting on any of these substances as 

 occasion arises. It is not surprising then that, with the more or 

 less imperfect methods at hand and with the use of such obscure 

 forms as '^Penicillium glaucum," which has served as a vehicle 

 for so many of these studies, many investigators believed that 

 they had found cases of qualitative enzyme regulation. Many of 

 these results appear to be due to the employment of chemical 

 methods, which were not accurate enough to detect enzymatic 

 action in slight amounts, while other results are clearly invali- 

 dated by the use of mixed cultures of unidentified or obscure or- 

 ganisms. Even so recent an investigator as Kylin (1914) em- 

 ploys "Penicillium glaucum" in certain experiments. It is now 

 well known that Penicillium glaucum is no more distinctive as a 

 fungus than ''green mould" and as Dox has suggested, the vari- 

 ous forms of Penicillium formerly grouped under this name are 

 so varied in their physiological reactions as to invalidate any 

 comparisons, based on species of Penicillium which were not 

 more definitely identified. 



Recent studies of qualitative enzyme regulation fail to reveal 

 more than one well authenticated case of qualitative enzyme regu- 

 lation. As has been suggested above, the work of Knudson 

 (1913) seems to leave little doubt that there exists a qualitative 

 regulation of tannase formation. It appears to be quite gener- 

 ally the impression of those authors, who have reviewed Knud- 

 son's work, that it was carefully done and that his results are 

 entirely dependable. 



The results of the experiments above described show very 

 clearly that there is no qualitative regulation of inulase forma- 

 tion in Aspergillus niger. Inulase is always produced in suffi- 

 cient quantities to be easily demonstrable. It should be said, 



