140 MICRO-ORGANISMS AND FERMENTATION. 



Yoghourt is a species of sour milk or thick milk prepared 

 in Turkey and Bulgaria. Sheep's or cow's milk is used, which 

 is boiled and reduced by evaporation to half its volume, then 

 cooled to 45 C., and the ferment " Maya " or " Podkoassa " 

 is added. This consists of milk residues from previous pre- 

 parations, dried under special conditions and ground, and 

 contains many species of bacteria. After a fermentation 

 lasting for nine to sixteen hours at a temperature of 40 C., 

 the Yoghourt is ready for consumption. It is more or less 

 solid, according to the degree of concentration, and possesses 

 a sourish aromatic taste. It is eaten cold, either alone or 

 with the addition of rice, bread, sugar, or fruit syrup. We 

 owe the first bacteriological investigation to Grigoroff. who 

 found three different lactic acid bacteria. The most important 

 is Bacillus A. (Bac. Bulgarus or Bulgaricus}. It forms long 

 motionless rods, often linked in chains, grows well on saccharine 

 substrata, has an optimum temperature of 45 C., and does 

 not multiply at room temperature. It produces alcohol, and 

 attacks lactose, mannite, dextrose, maltose, and Isevulose, 

 but not rhamnose, dulcite, and sorbite. Micrococcus B. occurs 

 as single cocci or diplococci. In addition to the above varieties 

 of sugar, it attacks rhamnose and glycerine. Streptobac. C. 

 forms short rods linked in chains. It attacks lactose, saccha- 

 rose, laevulose, and glycerine, but not maltose, mannite, 

 rhamnose, dulcite, or sorbite. The optimum temperature 

 for the last two species is 45 C., and they produce alcohol. 

 Other investigators (Maze) have only found two species of 

 bacteria. Luerssen and Kiihn, as well as Kunze, mention a 

 " granule bacillus," perhaps a variety of Bac, Bulgaricus. 

 Others have found yeast species to which they attach more or 

 less importance. Metschnikoff, Piorkowski, and Henneberg 

 have published further work regarding Yoghourt. 



The Ginger-beer Plant, which presents morphological 

 resemblances to the kephir ferment, has been examined both 

 botanically and biologically by Professor Marshall Ward. If 

 this ferment is introduced into saccharine solutions containing 

 ginger, it transforms them into an acid, effervescing beverage, 

 ginger-beer. When fresh, it forms solid, white, translucent 

 lumps, of irregular shape, brittle like dried jelly, varying in 



