300 PHARMACEUTICAL BACTERIOLOGY 



difficulty in examining them under the low power of the microscope. 

 Mount in water or in a weak solution (o.io per cent.) of caustic potash or 

 soda. In looking for yeasts and molds in liquids, centrifugalizing may 

 be desirable. Staining methods will rarely be necessary. 



While it is true that not all molds are pathogenic, yet it must be 

 remembered that many are decidedly so, besides most of them are very 

 objectionable on account of the disagreeable moldy odor and taste, 

 if for no other reason. Moldy food substances are not fit for consump- 

 tion and molds should not occur in any of the pharmaceuticals, syrups, 

 soda fountain preparations and fruit juices. Most of the yeasts are non- 

 pathogenic. The common yeast has even been used as an intestinal 

 disinfectant in typhoid fever, yet no preparations in the drug store should 

 be allowed to undergo yeast fermentation for the reason that the process 

 changes the quality and flavor of the substances thus attacked. Fruit 

 pulp, fruit juices and syrups of all kinds are peculiarly liable to the attacks 

 of the yeast organisms and every precaution should be taken to guard 

 against such infection. This is not a simple matter because the yeast 

 cells and the yeast spores are found everywhere and develop very readily 

 in all saccharine, slightly acid substances. Moist heat sterilization or 

 pasteurization are the most effectual means for preventing yeast fer- 

 mentations. 



The yeast cakes used by the housewife in making bread consist simply 

 of pure cultures of Saccharomyces. The cakes must be kept quite dry 

 and in the cold (ice chest) to prevent decomposition. Even under the 

 most favorable conditions they soon become worthless. As soon as the 

 cake is mixed with the bread dough with adequate warmth, the yeast cells 

 begin to feed upon the various available food substances present and 

 multiply rapidly (by budding), resulting in the formation of alcohol and 

 liberation of CO2 gas, which latter in an attempt to escape, causes the 

 so-called rising of the bread. If the dough is not thoroughly mixed, the gas 

 liberation is uneven and the bread will be unsatisfactory, because there 

 will be large cavities in some parts of the loaf and in other parts the loaf 

 will be solid. Bread must be baked quickly, after the rising has reached 

 the proper degree, otherwise the loaf will be flat and doughy. The house- 

 wife in the country simply prepares sour dough cakes which take the 

 place of the manufactured yeast cakes used in the city. In biscuit 

 making the desired CC>2 gas liberation is brought about by the use of 

 baking soda and sour milk or by means of baking powder alone. 



The alcoholic fermentation in the manufacture of beer is caused by the 

 several varieties and forms of Saccharomyces ceremsece (Torula cerevisea) . 

 In beer making, the barley grain is first acted upon by the starch enzyme 

 (diastase) which converts the starch into maltose (malt) and the maltose 



