62 OPT. A CTIY., HEREDITY AND ENVIRONMENT 



As to the problem of the possibility that different 

 isomers of lactic acid be produced when conditions of 

 cultivation are changed, the data of the literature have 

 for a long time been somewhat contradictory. 



a. I n f 1 u e n c e of General Culture Con- 

 ditions. It was Pere (1893) who claimed for the first 

 time that one and the same line of Bacterium coli^ in dif- 

 ferent culture conditions can produce the two inverse 

 forms of lactic acid (cf. also Pottevin, 1898, and Pere, 

 1898). But to what extent the strains of microbes used 

 by them were bacteriologically pure is not clear. 



Pederson, Peterson and Fred (1926) showed that in 

 mixed cultures of microbes consisting of producers of 

 the right and left isomers of lactic acid, one can often 

 observe a change in the form of the lactic acid produced 

 when the temperature, for example, is changed. How- 

 ever, in such cases, there is evidently no inverting mech- 

 anism in protoplasm. The species and strains of mi- 

 crobes which produce the right and the left isomers of 

 lactic acid possess different temperature optima of 

 growth and metabolism and consequently, in some con- 

 ditions of cultivation, the strains which produce the right 

 isomer and, in other conditions, those which give the left 

 isomer of lactic acid predominate. With microbic mate- 

 rial of a guaranteed purity having originated from one 

 cell, the possibility of inverting the lactic acid produced 

 has not been observed even in the most dift'erent culture 

 conditions, though the only isomer produced may subse- 

 quently undergo racemisation to various degrees. 



6. I n f 1 u e n c e of the Culture M e d i u m. 

 In the literature the work of Kayser (1894) is often re- 

 ferred to as confirming Pere 's data, whilst, as a matter of 



lit is to be pointed out that Bacterium coli does not cause a pure 

 lactic acid fermentation. Approximately half of the sugar is fermented 

 into lactic acid, the remainder is transformed into acetic acid, ethyl 

 alcohol, carbonic acid and hydrogen (Neuberg and Gorr, 1925). After 

 this was shown, the investigators began to work with true lactic-acid- 

 producers such as Lactobacillus. 



