218 Mutation in Micro-Organisms 



and that the dyes have a specific action upon the kinetonucleus 

 — but upon no other organ in tlie Trypanosome — and bring about its 

 destruction by autoxidation (Laveran and Roudskv). New races of 

 Trypanosomes are thus produced by modifying the individuals of the 

 old — not by selection. 



(B) Races of Trypanosomes without kinetonuclei possess a hnveied 

 virulence (Werbitzki, Laveran and Roudsky). 



By the action of various drugs and antibodies, races of Trypanosomes 

 may be obtained which are resistant to these substances (Ehrlicli, Mesnil 

 and Brimont, Breinl and Nierenstein, Levaditi and Twort, etc.). These 

 races subsequently breed true — though it may be a necessary condition 

 of this that they be kept in the same sort of host as that in which they 

 originally acquired their resistance. 



Races of Trypanosomes with a changed virulence are said to be pro- 

 duced by passage through certain animals (Wendelstadt and Fellmer) : 

 but this lias been denied (Gonder and Sieber, Laveran and Pettit). 



By treating T. leiuisi with arsenophenylglycin, a race may be 

 obtained which is resistant to this drug. This race breeds true — 

 retaining its resistance during numerous passages through untreated 

 rats. Resistant and non-resistant races remain unchanged, as regards 

 this character, when grown in artificial cultures. When the resistant 

 race undergoes a development in the louse — the exact nature of which 

 is not determined, though it is possibly sexual — resistance is gradually 

 lost, and the race returns to the original non-resistant condition 

 (Gonder). 



It has not been definitely determined whether resistance is brought 

 about by the direct action of the poison on the living Trypanosome 

 (Elirlich, etc.), or whether it is the result of selection (Levaditi, etc.). 



That some of the observations noticed in the course of this review 

 are of great interest, I think nobody would deny. And that they may 

 lead to a better comprehension of the phenomenon of mutation in 

 general is at least possible. In his Dresden address in 1911 Ehrlich 

 said: "...Aber, meine Herren, in der Natur ist nichts spontan, alles 

 hat seine Ursache, und wenn es sich um biologische Fragen handelt, 

 meistens eine chemische Ursache. ...So glaube ich, dass gerade diese 

 Studien an Parasiten, an kiinstlich herbeigefiihrten Mutationen durch 

 bestimmte biologische Eingriffe, deren Mechanismus genau erklarbar 

 ist, uns auch ein belles Licht iiber die so dunklen Fragen der Mutation 

 iiberhaupt bringen werden." (Ehrlich [1911], p. 95.) Though all may 



