C. DoBKi.L 347 



then, that the following remarks embody merely my own conclusions 

 drawn from the facts given in the body of this paper and from many 

 other related facts of which no mention has been made. They lay 

 claim to no finality, for the subject is not one upon which any final 

 judgment can yet be passed. 



If it be assumed that the statements made by various workers, 

 whose observations we have been considering, are correct, then the 

 following conclusions are justifiable. First, it seems established that 

 the Bacteria are subject to mutation — that is to say, in a given race 

 individuals may occur which differ from their fellows in their genetic 

 constitution. Individuals frequently occur which possess new structural 

 or functional features; and these features, though often the transient 

 peculiarities of the individual only, are in some cases transmitted to the 

 offspring for many successive generations. There is reason to suppose 

 that this phenomenon occurs in nature as well as in laboratory cultures. 

 The progeny of an organism which varies may thus constitute a new 

 race, in which every individual possesses the new character. We might 

 anticipate this, indeed, by consideration of the fact that the Bacteria 

 are non-sexual organisms. For a change in the genetic constitution of 

 the parent — where there is but one — appears likely to find expression 

 in all its offspring. There is no additional complication — in the trans- 

 mission of characters — introduced by a second parent. In sexually- 

 producing organisms, the genetic constitution of two parents must 

 always be considered, and there is not, therefore, such an obviously 

 direct relation between any one parent and its offspring as is seen in 

 non-sexual forms. 



It seems impossible to gauge the permanency of new races which 

 arise in this fashion. For there are indications that a new race may 

 give rise to other new races or to one indistinguishable from the old 

 race — all races arising in the same way. A race A may produce an 

 abnormal individual, which becomes the ancestor of a new race B. In 

 the same way, the race B may produce abnormal individuals giving 

 rise to races C, D...etc., of which one may be identical with A. There 

 is at present little to indicate the extent to which " reversion " of this 

 sort may occur. 



The factors which determine changes in genetic constitution are in 

 most cases obscure. It is impossible to say how most mutations have 

 been "caused." In Barber's experiments, the environment was the 

 same for all individuals — or at least he tried to make it so. The 

 factor which determined the appearance of individuals with an altered 



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