44 



PHYSIOLOGY OF NUTRITION 



fying the different yeasts, particularly in technical analysis for distinguishing 

 wild from cultivated forms. 



Saccharomyces pastorianus I. Hansen (Fig. 24). This is a bottom-fermenta- 

 tion yeast and consists mainly of elongated cells, but round and oval cells also 

 occur. This yeast is frequently present in the air in breweries. It imparts to 

 the beer a disagreeable, bitter taste and an unpleasant odor. 



Saccharomyces pastorianus III. Hansen. This top-fermentation ■ yeast 

 produces a turbid condition in beer (Fig. 25). 



Saccharomyces' anomalus Hansen. This species is distinguished by its char- 

 acteristic ascospores, which have the form of hemispheres, with projecting rims 

 at their bases (Fig. 26). 



Besides the species mentioned here, which are among those thoroughly 

 investigated by Hansen, a great many other yeasts, both wild and cultivated, 

 are known. Some of the cultivated 

 varieties are employed in the brew- 

 ing industry, some in distilleries, 

 some in the manufacture of berry 

 or fruit wines, and still others in the 

 preparation of compressed yeast for 

 bakers' use. 



The moulds (Fig. 27) are not 

 very exacting as to their nutrition. 



A B 



Fig. 26. — Saccharomyces anomalus. As- Fig. 27. — A, PenicilUum glaucum; B. Asper- 

 cospores. gillus glaiicus. A conidiophore, in each case. 



for they can grow upon a very great variety of materials. Among artificial 

 liquid media for mould culture, Raulin's^ solution is the best known; its 

 formula follows: 



Water 1500.0 g. 



Saccharose 70 . o g. 



Tartaric acid 4 . o g. 



Ammonium nitrate 4 . o g. 



Ammonium phosphate . . ; o . 6 g. 



Ammonium sulphate o . 25 g. 



Potassium silicate 0072. 



Potassium carbonate o6e 



Magnesium carbonate 0.42. 



Zinc sulphate ^ q_ „ 



Ferric sulphate ■ 0.07 g. 



Fermentation phenomena often accompany the nutrition of the moulds 

 and bacteria. There is still very little known concerning the nutrition of the 

 higher fungi. 



1 Raulin, Jules. Etudes chimiques sur la v«gMation. Ann. sci. nat. Bot. V, ii : 93-S99. 1869. 



