CONDITIONS OF LIFE OF THE BUDDING FUNGI. 521 



and yeast fungi. The latter do not bear such marked 

 concentration of the nutrient mixture as do the mould 

 fungi ; the optimum of the amount of water is, however, 

 equally dependent on the nature of the other nutrient 

 materials. Nutrient materials which are not very suit- 

 able require as a rule a great dilution (salts of ammonia 

 must not be present in more than 1 per cent.), while 

 sugar, for example, may be present in the nutrient 

 mixture up to 85 per cent, without leading to cessation 

 of the growth. 



With regard to the reaction, the yeast fungi resemble Thyeaction 

 the mould fungi in that they can bear a fairly markedly mixture. 

 acid reaction without harm ; but the upper limit of the 

 excess of acid is lower than in the case of the mould 

 fungi, so that by increasing the acidity of the material 

 (the addition of 5 per cent, of tartaric acid, or 1 per cent, 

 of phosphoric acid) the growth of the mould fungi, as 

 compared with that of the yeast fungi, is favoured. 

 Yeast seems to be very sensitive to an excess of alkali, 

 so that even traces of alkali can hinder growth. (Dumas, 

 Mayer.) 



3. Other Conditions of Life of the Yeast Fungi. 



Some of the other factors which can influence the energy 

 of growth of the fungi have also been investigated in the 

 case of yeast. Light and electricity are, so far as ex- Action of hij?h 

 periments have gone, without influence on the growth P rcssure - 

 of the yeast : in like manner, according to experiments 

 by Certes and Cochin,* a pressure of 300 to 400 atmo- 

 spheres maintained for several days did not injure yeast ; 

 under these circumstances, in fact, it was still able to 

 break up sugar into alcohol and carbonic acid. Hoppe- Action of 

 Seyler has observed that mechanical movement of the 

 nutrient solution acts in an unfavourable manner on 

 yeast ; but this investigation was limited to the question 

 of the fermentative activity of yeast, and besides, the 

 cultivations were much contaminated with bacteria. On 

 the other hand, Han sent has demonstrated, in a scries of 



* Compt. rend. soc. biol., 1884. 



f Meddedelser fra Carhberg Lab., vol. i., part 2. 



