THE VITAL PHENOMENA OF BACTERIA. 95 



groups, but that in combination, as for in- 

 stance with sodium sulphite (Na 2 SO 3 ), it loses 

 its poisonous quality and can serve as a food 

 for protoplasm. Pasteur long ago established 

 the same fact in the case of tartaric acid ; the 

 rule holds good likewise for succinic and malic 

 acids. Neelsen and I found the same thing 

 true of lactic acid, and I was eventually able to 

 make quite a simple solution with ammonium 

 lactate, in which the bacteria of " blue milk " 

 form synthetically the same pigment which 

 in milk they form analytically. (According 

 to Uschinsky, cholera and diphtheria germs 

 also form synthetic poisons in a similar solu- 

 tion.) In like fashion certain sugars may 

 afford fit material for this kind of synthesis. 



If we place the constitutional formula side 

 by side with the empirical, a difference becomes 

 at once manifest between such compounds as 

 tartaric acid or malic acid which contain 

 CHOH and succinic acid, and also between 

 lactic acid and propionic acid : 



Tartaric acid C 4 H 6 O 6 == CHOH.COOH CHOH.COOH. 

 Malic acid C 4 H 6 O 5 = CHOH.COOH CH 2 .COOH. 

 Succinic acid C 4 H 6 O 4 = COOH.CH 2 -CH 3 .COOH. 

 Lactic acid C 3 H 6 O 3 = CH 3 CHOH.COOH. 

 Propionic acid C 3 H 6 O 2 = CH 3 CH 2 COOH. 



Whereas tartaric, malic and lactic acids 

 contain the group CHOH and can readily 

 yield formaldehyde or the aldehyde group 



