112 BACTERIOLOGICAL CHEMISTRY 



able to Bynthesise uracil under aerobic conditions only. 

 It has been shown to be necessary for Lactobacillus 

 arabinosus, Leuconostoc mesenteroides and Group C 

 hemolytic streptococci. It can be replaced by orotic 

 acid (uracil 4-carboxylic acid) for the latter. Uracil 

 is not necessary as a growth factor for Group A hsemolytic 

 streptococci if carbon dioxide is present at a partial 

 pressure above 40 mm. of mercury. 



Folic acid. — Williams isolated folic acid from the 

 leaves of spinach and from yeast, liver and kidney. 

 It is possibly identical with, or forms a part of liver 

 " eluate factor." It occurs in most green leaves, including 

 grass. It contains vitamins Bio ^.nd B^ which are 

 necessary in the growth of cliicks and for the production 

 of feathers by chicks respectively. It also increases the 

 growth of rats. 



Folic acid is still of unknown constitution, but is 

 known to contain nitrogen but no sulphur or phosphorus. 

 It is said to have a molecular weight of about 500. An 

 active orange yellow crystalline substance of the com- 

 position C9H10N3O3, probably identical with vitamin Be, 

 the chick anti-anaemia factor, has been obtained from it. 

 The crystalline material induces half the maximum 

 growth of L. casei at a concentration of 0-00005 /xg./ml. 



Folic acid is required as a growth factor by many 

 lactic acid bacteria. In a concentration of 0-00012 

 /xg./ml. it gives half its maximum growth effect on Str. 

 lactis R. It also stimulates the growth of L, casei and 

 L. delbrilckii. A liver extract stimulating the growth 

 of L. casei E can be replaced by orotic acid, uracil-4 

 carboxylic acid, but not by uracil itseK. Orotic acid 

 may be a constituent of folic acid. There appear to be 

 at least two factors in folic acid required for bacterial 

 growth because, although an extract from spinach has 

 equal activity in supporting the groAvth of Str. lactis 

 and L. casei, extracts from liver and yeast have different 



