CONDITIONS OF GROWTH AND NUTRITION. 429 



On the other hand, the growth of this yeast is stimulated by 

 the admission of free oxygen (see p. 252, vol. ii.). This is apparent 

 from the behaviour of stab cultures in must gelatin, where vigorous 

 reproduction of the yeast cells is found to be confined to the upper 

 portion of the stab. More accurate information is afforded by an 

 experiment of ROHLING'S (I.), in which five different races of 

 Apiculatus yeast were sown in grape juice, one portion of the 

 latter being aerated in the fermentation vessels, the other not. 

 A difference in favour of the aerated yeast was already apparent 

 on the second day ; and at the close of fermentation the number 

 of cells in the aerated samples had increased from 3.3 to 9.3 times 

 as great (according to the race) as those in the unaerated samples. 

 This appears to harmonise with the observation that the percentage 

 of Apiculatus cells is occasionally much higher in the superficial 

 strata, and especially the head, of red wine must fermenting in 

 open vessels than it is in the lower layers that are poor in oxygen. 

 This need of oxygen is, of course, satisfied when the fungus is 

 grown on the surface of solid nutrient substrata ; and it is not 

 impossible that Sacch. apiculatus should gain the upper hand in 

 consequence of these specially favourable conditions. Considerable 

 accumulations of Apiculatus yeast, practically in the state of pure 

 cultures, are not infrequently found in the wounds of burst or 

 gnawed grapes, or in the tunnels eaten out in core fruit by apple- 

 roller larvse. 



The special conditions of nutrition of Apiculatus yeasts have not 

 been closely investigated to any extent. Its requirements in 

 respect of carbon are chiefly fulfilled at the expense of the hexoses 

 in the nutrient medium, but the fungus is incapable of fermenting 

 disaccharides, such as saccharose, or of utilising them for structural 

 purposes. More on this point will be found in the following 

 paragraph. The circumstance that the non-volatile organic acids 

 are consumed to a larger extent in cultures of Apiculatus yeast in 

 fruit juices than is the case with Sacch. ellipsoideuSj for example, 

 induces the idea that these acids may also be utilised as a source 

 of carbon for building up the cells ; but, on the other hand, it is 

 equally possible that the tartaric and malic acids in the instances 

 observed may have been decomposed by fermentation rather than 

 used for the purpose in question. In respect of nitrogen assimila- 

 tion, Apiculatus yeasts do not seem to differ from others ; at least 

 no statements have been published on this point. 



Sacch. apiculatus appears to be more susceptible to injurious 

 influences than the beery yeasts and the races of Sacch. ellipsoideus 

 occurring in wines. Its high susceptibility toward alcohol has 

 already been mentioned (p. 417, vol. ii.) ; but though a small per- 

 centage of alcohol is sufficient to retard growth, and apparently a 

 small additional quantity will arrest fermentation, a considerably 

 higher alcohol content would seem to be necessary in order to kill 

 the cells. In this connection, however, considerable differences are 



