362 
which can be isolated by the gelatin-must method. These organ- 
isms, according to this author, however, are not the active agents of 
a good industrial ferment. On the other hand, from such a ferment 
he was able to isolate the Lastobacillus fermentans. This organism 
when cultivated under good conditions yields only lactic acid and no 
volatile acids. The minimum temperature of its activity he found 
to be 25° C., the optimum temperature 41°-42° C., and the maximum 
temperature 50° C. These observations furnish an interesting con- 
firmation of the earlier work of Richet so far as the influence of 
temperature on the lactic fermentation is concerned. According 
to Beyerinck the lactic organisms studied by him can be mutually 
transformed into one another by cultivation. 
Heinemann (9) has called attention to the similarity existing 
between Bacillus acidi lactici (Hueppe and others) and Bacillus 
(lactis) aerogenes (Escherich) and also to the similarity of Bacillus 
lactis acidi (Leichmann and others), Streptococcus lacticus (Kruse) 
and Streptococcus pyogenes, and in a more recent communication 
(10) on the kinds of lactic acid produced by lactic acid bacteria, to 
the similarity of Streptococcus lacticus with Streptococcus pyogenes 
and of Bacillus acidi lactici with Bacillus aerogenes. It has been 
observed by this author that in the ordinary souring of milk, lactic 
acid is produced chiefly by Streptococcus lacticus and Bacillus aero- 
genes, and further, that the former organism predominates in ap- 
proximate proportion to the purity of the milk. Conn (11) also has 
shown that 95 to 100 per cent of all organisms in sour milk are of 
the Bacillus lactis acidi type (Streptococcus lacticus). 
It is now known that lactose (sugar of milk) is not directly fer- 
mentable, but must first be converted into the simpler sugars glucose 
and galactose. It has been shown by a number of investigators that 
many yeasts and bacteria produce an enzyme which is capable of 
effecting this hydrolysis, and Hirschfeld (12) has shown that in the 
souring of milk the lactic acid bacteria accomplish the inversion of 
lactose, and that this change takes place most rapidly in the first 
thirteen to twenty- four hours after the introduction of the organisms 
into the milk, the relative amounts of lactose inverted being: First 
day, 0.16; second day, 0.23; third day, 0.29. Finally in this connec- 
tion it has been shown by Buchner and Meisenheimer ( 13 ) , and inde- 
pendently by Herzog (14), that an enzyme can be extracted from 
certain of the lactic-acid- forming bacteria, which in the absence of 
organisms is able to transform lactose and cane sugar into lactic acid. 
Buchner and Meisenheimer extracted the ferment from Bacillus Del- 
bruecki (Leichmann), whereas in his experiments Herzog employed 
the Bacterium acidi lactici. On the other hand Beyerinck (8) is of 
the opinion that the production of lactic acid by the lactic acid 
bacteria is not a mere enzymic function, but a catabolic process. 
