212 Mutation in Micro- Organisms 



Herpetomonas jaculum respectively. It is unfortunate that the origin of 

 these forms is as yet quite unknown ^ Probably they were merely 

 degenerate individuals. 



B. Physiological Mutations. 



It has now been known for some years — largely through the work 

 of Ehrlich and his collaborators — that drugs and antibodies may modify 

 profoundly the physiological properties of Trypanosomes. As early as 

 1907, Ehrlich showed that treatment of Trypanosome-infected animals 

 with atoxyP might cause — under certain conditions — the Trypanosomes 

 to acquire an immunity to the drug. By subjecting the Trypanosomes to 

 the action of minute but increasing quantities of atoxyl or other drugs, 

 Ehrlich has succeeded in obtaining strains of the parasites which are 

 highly resistant^ to these poisons. In 1909 he stated that he had pro- 

 duced an arsenic-resistant strain of T. brucei, which had, in the course 

 of three years, undergone passages through some four hundred untreated 

 animals — without any loss of resistance to arsenic. Many similar ob- 

 servations have since been recorded, so that it may now be stated as 

 a fact that physiologically modified races of Trypanosomes can be made 

 by artificial means from the races which occur normally in nature. 



Mesnil and Brimont (1908) also succeeded in obtaining a race of 

 Trypanosomes resistant to atoxyl. But they pointed out that the re- 

 sistance was only manifested " in a given organism " {i.e. host). More 

 definite in this respect, however, were the statements of Breinl and 

 Nierenstein (1908)^ From inoculation experiments, they concluded 

 that a Trypanosome's resistance to the drug is manifested in that 



^ It should be remembered that Trypanosomes which have grown in artificial culture 

 media frequently display morphological peculiarities — as regards size, shape, relative 

 position of nuclei, etc. These modifications are, however, transitory : they do not 

 persist after the organisms have been reinoculated into the animals which are their 

 normal hosts. 



2 Atoxyl is sodium arsanilate — the Na salt of jj-aminophenyl-arsenic acid (Ehrlich and 

 Bertheim). 



* A Trypanosome which tolerates the action of a drug is generally said to be " fast " 

 to the drug in question, e.g. a Trypanosome which has been rendered tolerant to atoxyl or 

 other organic arsenicals is spoken of as "arsenic- fast." The word "fast" has, however, 

 an older and very different usage in bacteriology. For instance, tubercle Bacilli — and 

 certain others — are called "acid-fast." This does not mean that the living organisms 

 tolerate, or are resistant to, acids : it means that dead organisms when stained with 

 carbol-fuchsin are stained "fast" (in the dyer's sense) against mineral acids. I therefore 

 prefer to use "resistant" rather than "fast" when discussing the phenomena of living 

 Trypanosomes. 



* These workers, it may be noted, give an incorrect account of the results of Mesnil and 

 Brimont. 



