150 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



added to neutralise the free acid as it is formed, calcium 

 lactate being the result. 



Under certain conditions a further decomposition of the 

 lactic acid occurs, forming butyric acid according to the follow- 

 ing equation : 



2C 3 H 6 3 = C 4 H 8 2 + 2C0 2 + 2H 2 



Lactic acid Butyric acid Carbonic Free 



acid gas hydrogen 



This butyric fermentation is brought about by a number 

 of organisms, some of which are anaerobic. 



The equation on p. 149, representing the formation of 

 lactic acid from a hexose, must only be taken as a part of what 

 actually occurs. Moreover, in the case of lactic acid, there are 

 in this simple equation further possibilities because, as already 

 explained, lactic acid contains an asymmetric carbon atom, 

 and therefore exists in three possible forms, viz., a right-handed 

 and left-handed, and an inactive modification. Which of these 

 forms remains at the end of the reaction depends on the con- 

 ditions of experiment. It will be remembered that the lactic 

 acid above referred to is the a-acid CH 3 C HOHC0 2 H, the 

 central carbon atom being asymmetric ; the inactive form is 

 almost always met with as the result of lactic acid fermenta- 

 tion. 1 There is also, it may be remembered, another form of 

 lactic acid, viz. /3-lactic acid, CH 2 OHCH 2 C0 2 H, the production 

 of which is a further possibility. Its production has been 

 stated to occur when inosite is fermented r.nder certain condi- 

 tions,but the evidence of its occurrence is somewhat conflicting. 



The chemical interest of the lactic acid fermentation centres, 

 therefore, generally round the conditions of production of the 

 right-handed and left-handed modifications, and reference may 

 therefore be made to the experiments of Frankland and 

 MacGregor, which indicate that the inactive or racemic form 

 of acid may in certain cases be produced, after which a pre- 

 ferential decomposition of one of the modifications takes place. 



Frankland and MacGregor experimented with a bacterial 



1 An active form known as sarcolactic acid can be obtained from meat 

 juice, 



