BIOLOGICAL RELATIONSHIPS OF YEAST. 271 



widely distributed in nature, and that their germs are present 

 in atmospheric air, in dust, and in vegetable matter, and that 

 their breeding places are specially to be sought in the excre- 

 ment of herbivorous animals. Here they can exercise their 

 fermentative power. It will be seen from what follows that 

 this view can no longer be accepted. It is true, as the author 

 has proved by his own investigations, that the excrement of 

 herbivorous birds contains numerous budding fungi, and 

 amongst them Saccharomycetes, but their breeding places must 

 be sought in quite a different direction. 



In 1876 and 1879 Pasteur published complete memoirs 

 regarding the occurrence of yeasts on grapes, and stated 

 that they were to be found only on ripe grapes. At the 

 same time he did not succeed in answering the important 

 question as to where the yeast fungi found a habitat during 

 the remaining part of the year. He expressed the view that 

 Dematium pullulans, which is found everywhere on grapes ,. 

 lives through the winter in the form of thick-walled and 

 coloured resting-cells, and produces new yeast cells in the 

 following summer, but it is now recognised that these budding 

 cells are not wine-yeast cells. On the other hand, it was shown 

 by the author in 1895 that other mould forms occurring on 

 grapes, which resemble Dematium, but do not possess thick- 

 walled resting-cells (Fig. 45), produce internal spores which 

 develop budding Saccharomyces cells. What part these moulds 

 play in the preservation of the yeast vegetation has not yet 

 been determined. 



Great uncertainty still existed regarding the most important 

 question as to where the yeast remained during the different 

 seasons of the year. It was established for a single species 

 by E. C. Hansen in 1880-81, and his further researches, of a 

 very detailed and fundamental character, have cleared up the 

 question for so many other species that this important phase 

 of the biology of yeasts is now fully understood. The researches 

 of Hansen were first carried out on the small lemon-shaped 

 yeast-fungus S. apiculatus, which always appears in the earliest 

 stage of wine fermentation. By a microscopical examination 

 and culture experiments it was shown that during the summer 

 months the organism appeared in vast quantities with the 



