320 BACTERIOLOGICAL CHEMISTRY 



neutral ov faintly acid ; the fei-nientatioJi is complete in 

 four to six days. The calcium lactate is recovered from 

 the mash by filtration, evaporation of the filtrate and 

 crystallisation. The calcium is removed as calcium 

 sulphate by addition of sulphuric acid and the lactic acid 

 solution concentrated to about 50 per cent. 



Lactic acid is largely used for " deliming " hides, that 

 is, for removing the lime employed in the " dehairing " 

 process preparatory to tanning, and for softening hides. 

 It is used extensively in the textile industry as a mordant 

 in dyeing and for the acid dyeing of wool. It is much 

 used in the form of its ethyl ester as a plasticiser in resins 

 and lacquers and as a solvent for cellulose finishes. Lactic 

 acid is finding increasing use also as a flavouring agent 

 and acidulant in the preparation of " soft " drinks and 

 food products. 



The initial stages of lactic acid fermentation are very 

 probably the same as those of alcoholic fermentation, 

 involving phosphorylation and co -enzyme I. If co- 

 enzyme I is removed from lactic acid bacteria by washing 

 they no longer produce lactic acid. Lactic acid fermenta- 

 tion is accelerated by the addition of phosphates in a 

 manner analogous to that of alcoholic fermentation. 

 Two mechanisms are possible for lactic acid fermentation, 

 the first A, going through pyruvic acid and the second, 

 B, through methylglyoxal. 



zymohexase 



A. (1) Hexosediphosphate > Dihydroxyacetone phosphate + 3- 



phospho -gly ceralde hy de . 



isomerase 



(2) Dihydroxyacetone phosphate ■ > 3-phosphoglyceraldehyde 



(3) 3 -Phosi)hogly ceralde hyde + phosphate + co-enzyme I 



triosephosphorylase , , , , 



> 1 : 3-(liphosphoglyceric acid + dihydroco- 



enzynie I. 



(4) 1 : 3-I)iphosphoglyceric acid + adenosine diphosphate > 3-phos- 



phoglyceric acid + adenosine trijjhosphate. 



