26 OPTICAL ACTIVITY OF BIOL. MATERIAL 



Katagiri and Katahara (1937) have shown that, in bac- 

 teria, optically pure lactic acid is formed first and that it 

 racemises later under the influence of some environmental 

 conditions. 



Inactive lactic acid was also recorded in comparatively 

 rare post mortem observations in animals (Morishima, 

 1900). 



As is well known, dextrorotatory lactic acid is found in 

 vertebrates and in different organs of invertebrates and 

 racemisation is rare. The tendency has been, for a long- 

 time, to explain the presence of this racemic lactic acid 

 (especially in the case of bacterial fermentation) by the 

 inactivity of the intermediate product, methylglyoxal, 

 which has no asymmetric carbon atom and from which 

 racemic lactic acid could be formed without the participa- 

 tion of an optically active enzyme. But, at present, 

 methylglyoxal is no longer considered an intermediate 

 product in the transformation of the carbohydrates, and, 

 besides, the thorough investigations of Katagiri and Kata- 

 hara (1937) have demonstrated an initial formation of 

 active lactic acid, which racemises later. 



Racemisation of the secondary substances after they are 

 detached from the primary asymmetric complex takes place 

 also in the glucosides which, in plants, play the part of 

 storage material. The nitrite of mandelic acid which is 

 enzymatically synthesised in plants in the relatively pure 

 dextrorotatory form is subsequently racemisecl, and in the 

 leaves of Primus laurocerasus, a glucoside of racemic dl- 

 nitrile is found (Kuhn, 1936; this subject will be examined 

 in detail elsewhere). 



The terpenes which, in general, represent vegetable 

 secretions but on whose origin and physiological function 

 much remains to be investigated are also often found in 

 plants in the racemic state. For instance, racemic limo- 

 nene or dipentene has been observed in Pinus silvestris, 

 Lauriis camphora, Valeriana ojjic'malis and many others 

 (Bartelt, 1910, names 16 of them). But optically active 

 limonene as well is found in the same or similar kinds of 



