6 A MANUAL OF BACTERIOLOGY 



Dunbar, 1 as the result of a series of experiments con- 

 ducted over a long period and with every care to prevent 

 contamination, came to the conclusion that the bacteria 

 are not an independent group of organisms, but that the 

 bacteria, yeasts, and moulds are stages in the life-history 

 of green algae. A culture of a single-celled alga belonging 

 to the Palmellacea was obtained, but by modifying the 

 culture medium in which a pure culture of the alga was 

 growing, by the addition of acid, alkali, or traces of copper 

 salts, other organisms, generally bacteria, occasionally 

 moulds and yeasts, and even spirochaetes, made their 

 appearance. Granting that there is no flaw in the obser- 

 vations, and every care seems to have been taken to 

 exclude contamination, etc., the results are susceptible 

 of another explanation, viz. that the secondary growths 

 were derived by transformation of the algal cells, in fact 

 by the phenomenon oi hetero -genesis which Bastian 

 claimed to occur. 



Bacteria undoubtedly exhibit variations and muta- 

 tions, not only in morphology (see p. 16) but also in 

 function. Thus pathogenic organisms may become non- 

 pathogenic, and Twort succeeded in training B. typhosus 

 to ferment lactose, which ordinarily it does not. Some 

 experiments by Horrocks suggest that the B. typhosus 

 may, by symbiosis with B. coli, be converted into B. 

 alkaligenes, and Revis found that many variations occur 

 with coliform organisms as a result of cultivating in 

 malachite green media, etc. 2 



As a result of exposure of sporing anthrax to ultra- 

 violet rays, Mme. Henri 3 states that stable coccoid and 

 thin Gram-negative filamentous forms are obtained. 



1 See Journ. Roy. Inst. Pub, Health, vol. xv, No. 11, 1907, p. 679, 



2 Proc. Roy. Soc. Lond., B, vol. 85, p. 192, and vol. 86, p. 373 ; Centr. f. 

 Bald., Abt. II, 1912 and 1913. 



3 Comp. Rend. Acad. 8c. t vol. 158, No. 14, 1914, p. 1032. 



