124 



view was generally accepted by all investigators in this field until 

 Orla-Jensen recently proved that ammonium nitrogen is also as- 

 similated, provided that suitable activators of an organic nature are 

 present. 



Finally, Beijerinck expresses the opinion that the production of 

 mannitol from laevulose is another general property of lactic acid 

 bacteria. Nowadays we know that this ability is restricted to the sub- 

 group of the so-called heterofermentative lactic acid bacteria. Yet it 

 must be deemed to be a great merit of Beijerinck that he fully 

 realized that the said mannitol production is not due to the action of a 

 separate group of specific bacteria, as is suggested by the term "fer- 

 ment mannitique", of ten used by French investigators, even now- 

 adays. 



Six years later Beijerinck published another fundamentally 

 important paper on the group under review, this time dealing with 

 the various lactic acid bacteria occurring in milk and in milk pro- 

 ducts i). 



This presented an even more systematic survey of the properties of 

 the true lactic acid bacteria. In addition to the characters already 

 discussed Beijerinck laid emphasis upon the absence of spore-form- 

 ing ability. He also pointed out, however, that the cells of the lactic 

 acid bacteria are much more thermo-resistant than those of other non- 

 spore-forming bacteria, so that by heating to 65-75° C. during a suita- 

 ble period a separation of the lactic acid bacteria from the other non- 

 spore-forming groups can be carried through. For this procedure he 

 coins the new term "lacticisation", a term which, however, has not 

 found acceptance. 



Beijerinck also expressed the opinion that all lactic acid bacteria 

 have the ability to decompose the glucosides aesculin and indican 

 (emulsin reaction) . For the detection of this property he devised very 

 simple and elegant methods2). In the light of our present-day 

 knowledge it seems doubtful whether, indeed, the said property is a 

 universal characteristic of lactic acid bacteria. It seems more probable 

 that the reaction is restricted to the homofermentative subgroup, as 

 also holds for the decomposition of another glucoside, salicin. 



The greater part of the paper is devoted to a detailed description of 

 the different types of lactic acid bacteria which are obtained in ac- 

 cumulation experiments with milk at different temperature ranges. A 

 final chapter deals exhaustively with the lactic acid bacteria present 

 in yoghurt, a preparation which at that time had just come into vogue 

 owing to Metchnikoff's suggestive theory of auto-intoxication 

 caused by the normal intestinal flora. 



1) Proc. Kon. Akad. v. Wet. Amsterdam 10, 17, 1907. 



2) As f ar as aesculin decomposition is concerned the observations ware due to Beije- 

 rinck's colleague ter Meulen, who had previously made extensive studies on gluco- 

 side decomposition. 



