VIII, B, 6 Barber: Dysentery Bacilli 553 



in lower organisms. In all cases, we may conceive that, what- 

 ever the stimulus, the mutation consists in the change of latent 

 hereditary units (Progenen) to active ones (Genen), whether 

 the change appears as an advance or an atavism. 



The maltose-fermenting race of dysentery bacilli isolated by 

 me was obtained from ordinary agar cultures, not from sec- 

 ondary colonies on maltose. The appearance of the charac- 

 teristic on a maltose-free medium would point to a variation of 

 a nonadaptive character, and would indicate that we have to 

 do with a parent race originally non-stable with regard to maltose 

 fermentation. The new characteristic is fully formed at the 

 start, and persists through many generations ; but the compara- 

 tively large percentage of acid-forming cells in the first series 

 and the apparent instability of the parent culture might exclude 

 this variation from the catagory of mutation. It is true that 

 any cell of the non-maltose fermenting type may originate an 

 acid-producing race ; but many generations may intervene before 

 the maltose-fermenting cells arise. The final decision in this 

 matter must depend upon the definition of the term mutation. 



With regard to the other form of variation described here, that 

 appearing in strain 42, we certainly approach more nearly to 

 the characteristics of a true mutation. The variation certainly 

 appears suddenly and fully formed. It appears in a relatively 

 small number of individuals, it is not adaptive, and the new 

 characteristics are transmissible to offspring through many 

 generations. This new race is to be compared with the one 

 described by me in Bacterium coli, in which the selection of 

 certain long threads gave rise to races permanently different 

 from the parent stock. There is the possibility of regarding 

 both cases as degenerations, but after they became started both 

 types showed as much vegetative vigor as the parent race, while 

 still retaining new characteristics. Whether within the strict 

 scope of the definition of mutation or not, both cases seem com- 

 parable to sports appearing vegetatively on higher plants and 

 capable of indefinite propagation. Some of these variations may 

 at first show less vegetative vigor than the parent and be none 

 the less regarded as true sports. 



SUMMARY 



1. From a culture of Bacillus dysenterix, Flexner type, derived 

 from a single cell, 3 series of single-cell isolations were made at 

 intervals of about five months. The first series gave 5 maltose- 

 fermenting variants out of 21 isolations ; the second, 5 out of 60 ; 



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