INDUCED ENZYME FORMATION 



the possession of the inducer. The possibiHty is therefore pro- 

 vided for a third template type, neither active nor inactive, 

 possessing the second property but not the galactose. A de- 

 scription is thus provided for the "convertible" template, which 

 becomes stabilized in the active form on the addition of inducer. 



We now turn to a consideration of the likely nature of this 

 ''second property" possessed in common by active and "con- 

 vertible" templates, but lacking in the inactive variety. For 

 simplicity and ease of following the argument, we may here 

 summarize the properties which any model constructed on the 

 basis of the above discussion must exhibit. 



/. Each cell contains a certain number of templates 

 specific for the synthesis of some enzyme of the galactose system. 

 They may exist in "active," "inactive," or "convertible" forms. 



2. A cell containing one or more active or convertible 

 templates will give rise within a few hours of growth in a galac- 

 tose medium to progeny in which most or all of the templates are 

 active. 



3. A cell containing no active or convertible templates 

 may grow for many generations on galactose without any tem- 

 plate ever becoming active. If activation does occur it is a 

 rare event. It is heritable on the cellular level as required by 

 property (2). 



4. Active templates differ from convertible ones in that 

 the former contain galactose. Convertible templates are readily 

 transformed to active ones by the addition of galactose. 



5. Active templates form the enzyme mentioned under 

 (7) ; inactive ones do not. 



From properties (2) and (J) it is clear that the presence of 

 some active templates in the cell greatly accelerate the activa- 

 tion of other templates. Whether this includes other templates 

 already present or only those subsequently formed is not de- 

 ducible from the data. The question is, however, how this 

 activation might take place. 



The two simplest possibilities are {a) the active templates 

 self-duplicate, the new ones being, so to speak, descended from 



143 



