C. DOBKLL 343 



which formed spores and others which did not. Barber isolated 

 a number of individuals of the latter type, and cultivated them 

 further. In only one instance, however, did he succeed in thus 

 obtaining a permanently asporogenic race. In all other cases the 

 isolated individuals gave rise to spore-forming colonies. The mutation 

 in this case may be called spontaneous. There is nothing to indicate 

 that it was due to any particular external conditions. 



Some remarkable statements concerning "mutations" in the cholera 

 vibrio have been made recently by Baerthlein (1911), and a further 

 contribution to the same subject has just been made by Eisenberg 

 (1912 a). It is said that pure cultures of this organism when plated 

 out on agar constantly give rise to several different kinds of colonies — 

 produced by " mutations " from the original race. The " mutated " 

 forms are said to be in some cases constant, in others inconstant or 

 capable of undergoing further " mutations " or " reversions." The facts 

 at present available seem so confusing, and sometimes so contradictory, 

 that I think no very satisfactory conclusions can yet be drawn from 

 them. I will therefore merely refer the reader to this work without 

 attempting to discuss it here. 



It seems legitimate to conclude from the foregoing facts that some 

 races of bacteria are able permanently to acquire new characters under 

 certain conditions : and also that they may in a similar manner lose 

 these characters subsequently. So far we have considered the behaviour 

 of bacteria under experimental conditions only, but one is naturally led 

 to inquire whether similar changes occur in nature. The answer to 

 this question is obviously of the greatest importance not only to the 

 biologist but also to the medical man : and it has frequently been given 

 both in the negative and in the affirmative. A little reflection on the 

 problems involved in the question will suffice to make this easily 

 explicable. It is, in fact, at present impossible to answer the question 

 in other than a most tentative manner. Nevertheless, a few cases have 

 been recorded which seem to throw some light on the matter. With 

 one of the best and most recent of these I will conclude the present 

 section. 



S^rensen (1 91 2) has just recorded the following remarkable facts. 

 A patient suffering from glycosuria, developed in addition pneumaturia. 

 This was found to be caused by a peculiar bacillus (B. pneumaturiae) 

 which had gained access to the bladder, and by fermenting the sugar 

 there produced large quantities of gas. The organisms were isolated 



