115 



worthy is the demonstration with the aid of the luminous-bacteria- 

 plate method that the fermentation of the lactose is preceded by a 

 splitting of this sugar into its hexose constituents. In addition he 

 showed the same to be true of another lactose-fermenting yeast always 

 found in Edam cheese, to which organism he gave the name Saccharo- 

 myces tyrocola. 



These observations were presented in even more detail in a second 

 paper i), and in it BEIJERINCK coined the term "lactase" for the 

 enzyme which brings about the hydrolysis of lactose. Experimental 

 proof was given that this enzyme is excreted by the yeast cells into 

 the culture medium, and BEIJERINCK may, therefore, be rightly con- 

 sidered as the discoverer of lactase. 



In 1892 a study 2 ) was published on the nutritional requirements of 

 the film-producing yeast species, at that time known as Saccharomyces 

 mycoderma. This paper is remarkable because in it was made the first 

 attempt to carry through a differentiation of various yeast species on 

 the basis of their different behaviour towards sugars. Moreover, it is 

 shown that these oxidizing yeast species are also able to develop on 

 various organic substrates other than sugars, as for instance glycerol, 

 succinate and acetate. This is a fact too often neglected even now- 

 adays. Attention was also given to the suitability of various single 

 compounds to act as sole nitrogen source for the development of 

 various yeasts. Finally, it was emphasized, that under conditions of 

 anaerobiosis also the oxidizing yeast is capable of bringing about a 

 regular alcoholic fermentation ; this phenomenon was discussed in the 

 light of PASTEUR'S fermentation theory. 



The discovery made in 1 894 of the new yeast species Schizosaccha- 

 romycesoctosporus, isolated from raisins, may be deemed to be of great 

 importance 3 ) . Here for the first time a description was given of a yeast 

 under suitable conditions regularly producing eight endospores. This 

 fact brought final proof for the correctness of DE BARY'S and REESS' 

 assumption that the spore-forming yeasts had to be classified with the 

 Ascornycetes. 



In the hands of GUILLIERMOND some years later this species was to 

 give the first clue to the cytology and phylogeny of the whole group 

 of yeasts. The direct inducement to these investigations may well have 

 been BEIJERINCK'S statement that in contrast to what holds for 

 Saccharomyces species - the occurrence of a nucleus in the cells of 

 Schizosaccharomyces octosporus can be observed beyond any doubt. 

 BEIJERINCK had already noted that a nuclear division into eight pre- 

 cedes the formation of the eight ascospores. Amongst the physiological 

 properties of the new species, BEIJERINCK stressed its ability to fer- 



1) Centralbl. f. Bakt. u. Parasitenk. 6, 44, 1889. 



2) Centralbl. f. Bakt. u. Parasitenk. 11, 68, 1892. 



3) Centralbl. f. Bakt. u. Parasitenk. 16, 49, 1894. 



