RESEARCHES ON YEASTS. 93 



attenuation, in many cases at least, go together. According 

 to the treatment to which a yeast is subjected in the laboratory, 

 one and the same species may be made to clarify well or 

 badly in the brewery ; it can be made to behave somewhat dif- 

 ferently according to the conditions of nutrition under which 

 the numberless generations of cells of which it is composed 

 have been cultivated. I will not, however, here enter into 

 general considerations of interesting theoretical possibilities 

 which speculation suggests, but I will briefly state some of 

 the most important results to which my experiments have led. 

 When in 1883 I began my experiments in the brewery 

 with the species named by me Carlsberg yeast No. I, I at 

 once found that a bad result was obtained when the yeast 

 had been cultivated in a wort which had not been aerated. 

 If the wort is not aerated directly after sterilisation, the 

 containing flasks must be set aside for a length of time, in 

 order that the wort may become gradually aerated by the 

 air which slowly gains access to it through the bent tubes 

 or through the cotton-wool plugs. I have already pointed 

 out how important it may be that the first portion of the 

 yeast, even in the laboratory, is grown in well aerated wort. 

 The following experiments were carried out in 1884, and 

 were subsequently repeated in 1 890. The yeasts employed 

 were Carlsberg yeast No. I and Carlsberg yeast No. 2, both 

 in pure culture. In one series of experiments non-aerated, 

 and in the other normal aerated wort was employed ; it 

 was sterilised, and was the same as that generally used in 

 the manufacture of ordinary lager beer (13*5 per cent. Ball.). 

 The wort was in Pasteur vessels, each of which contained 

 i 5 hectoliters, and these stood in a room, the temperature 

 of which was 10-12 C. Each species of yeast was intro- 

 duced into a separate vessel, and the amount employed was 

 o f 5 kilogram of moderately thin yeast. In all cases the 

 brightening was unsatisfactory, but the yeast produced 

 behaved differently in the two series of experiments. The 



