OPTICAL ArTTYTTY OF BIOL. MATERIAL 23 



The pveparation from cow's milk and that from the 

 bulbs of Dahlia show a weak racemisatioii as a result of 

 the treatment, while the preparation from the embryos of 

 Lupinus is optically pure ; the autolysis procedure used in 

 this last case prevents racemisation. 



One can, at present, consider as an established fact that 

 all amino-acids entering into the composition of proto- 

 plasmic proteins are optically pure ; not a single exception 

 is known/ 



The fats or lecithins, which contain nitrogen and phos- 

 phorus, and which are considered integral constituents of 

 the fundamental units of protoplasm, are also optically 

 pure, as it was, for instance, established by the investiga- 

 tions of Mayer (1906). 



Among primary substances, the carbohydrates, as well, 

 are for the most part optically pure. Brown and Morris 

 (1893) have shown in an extensive investigation that glu- 

 cose and other sugars are found in the optically pure form 

 in the leaves of the plant Tropaeolum majus. 



An interesting exception to the general rule has been 

 observed in sugars. Neuberg (1900) found in the human 

 organism optically inactive, racemic sugar under patho- 

 logical conditions. Salkowsky (1892), who had discovered 

 that in this case a pentose (arabinose) is excreted in urine, 

 instead of glucose as it happens in glucosuria, called the 

 disease pentosuria. Neuberg established that the arabi- 

 nose excreted in urine is optically inactive. These obser- 

 vations were later confirmed by a number of other physi- 

 ologists. In what relation the inactive arabinose stands 

 to the active arabinose entering into the composition of the 

 nucleo-proteids of our body is at present unknown. 



Racemic sugar, dl-galactose, was also found in plants. 

 Oshima and Tollens (1901) isolated it from the Japanese 

 marine alga, Porphyra laciniafa. 



The presence of racemic sugars in plants and animals is 



1 It seems preferable, for the present, to suspend judgment on the recent 

 data of Kogl and Erxleben (1939) concerning partial racemisation of some 

 amino-acids in proteins of malignant cells. 



