C. DOBELL 387 



The chang'es undergone by organisms of the voli-typhosus group 

 appear to be in all cases of the same nature — so far as they have 

 been considered up to this point. All the changes appear to be 

 direct adaptations. An organism comes in contact with a new sugar 

 which it is unable to use for its own growth. It then changes itself 

 so that it can split the sugar — the change being thus definite, towards 

 a definite end, and apparently purposive. There appears to be a defi- 

 nite relation between the sugar and the mutation. In some other 

 cases, however, this relation is not obvious. Two instances of this 

 may be briefly mentioned. B. typhosus when grown on glycerin-agar 

 produces acid. A closely related form {B. metatypld), however, according 

 to Mandelbaum (1912) produces alkali instead. But if luetatyphi is 

 grown for a long time on this medium, it forms nodules in the parent 

 colonies — exactly like those produced in colonies of B. coli mutabile. 

 The individuals in these nodules are typical acid-producing forms 

 indistinguishable from ordinary B. typhosus. They do not revert to 

 the alkali-producing form. In other words, metatyphi mutates partially 

 into typhosus^. 



Revis (1911) has studied certain coli-typhosus organisms which 

 produce both acid and gas when grown in peptone broth containing 

 certain sugars or polyhydric alcohols (e.g. lactose). He was able 

 gradually to acclimatize these organisms to a medium containing 

 O'l 7o of malachite green. The organisms after this, however, had 

 permanently lost the power of producing gas in the original media, 

 though they could still form acid. The dye appears therefore to 

 have made a lasting change in their method of attacking certain 

 food-substances". 



It will be seen, I think, that in these two cases just quoted the 

 changes produced are not obviously of an adaptive nature — though 

 possibly a greater knowledge of the chemistry of the matter might 

 bring them into line with the preceding observations. But in the 

 cases which we are now about to consider the changes produced seem 

 to be quite definitely not adaptive. The mutations concern pigment- 

 production — not ferment-production ^ 



• Mandelbaum calls it a " remutation " or "atavistic throw-back" because he believes 

 that metatyphi has arisen by mutation from typhosus. 



" Eevis (1911) recorded only a single instance in which this change was observable. 

 But in a subsequent paper (Revis, 1912) he states that he has been able to effect the same 

 change in two other races of similar organisms. 



' For earlier work on both these subjects consult Pringsheim (1910). Here also will 

 be found an account of similar changes in ferment-production among Fungi. 



