176 MICRO-ORGANISMS AND FERMENTATION. 



to each individual department of our industry. Numerous 

 instances were met with in which even slightly noticeable 

 characters, manifested through taste or smell, remain inherent 

 after several years' preservation of the growth and a suitably 

 renewed development of the culture under favourable circum- 

 stances. 



(g) Variations in the species of the Saccharomycetes. 

 HANSEN'S numerous investigations have proved that the 

 Saccharomycetes are affected in various ways by external in- 

 fluences. From the results recorded in the previous sections, 

 we are perfectly justified in saying that there are a number of 

 species, not only of the so-called wild yeasts (species which 

 were formerly described under the general names Sacch. 

 Pastorianus, Sacch. ellipsoideus, etc.), but also of well- 

 characterised top- and bottom-yeasts, which are employed in 

 practice. It is a point of great practical interest that 

 species cultivated in beer-wort, the cultivation of which has 

 been uninterruptedly continued for several years, have shown 

 only the slightest changes, or none at all. While HANSEN 

 was arriving at these results, he discovered that it was 

 possible, by suitable treatment, to produce variations in 

 different directions ; and that in this respect, also, the indi- 

 vidual peculiarities of the cells in an absolutely pure culture 

 may assert themselves. Some of these changes are only 

 temporary, and disappear under suitable treatment, while 

 the species reassumes its original character. Others are 

 more deeply seated, and it is then only under especially 

 favourable conditions that the culture can be deprived of 

 its newly-acquired properties. In certain cases it was found 

 impossible, even after years of methodical treatment, to 

 re-convert a growth into its original state. 



1. As we have stated, the data regarding the time required 

 for the appearance of the first indications of spore-formation in 

 the six species previously described, are subject to the condition 

 that the growth has been previously cultivated in wort for 24 

 hours at a temperature of 25 C. Simultaneously with the 

 publication of his temperature curves (1883), HANSEN found 

 that cultures which had been grown in wort at the above 

 temperature, but for two days instead of one, developed spores 



