234 



PHARMACEUTICAL BACTERIOLOGY 



Occasionally the vinegar loses its acidity, This is due to the invasion 

 of a bacillus {B. xylenum) which, in the presence of oxygen, splits up the 

 acetic acid into other compounds. This change can be prevented by 

 excluding air from the containers. Vinegar should contain 4 to 4.5 

 per cent, of acetic acid (the legal standard). 



Beer and Wine Organisms. — We have elsewhere briefly outUned 

 the manufacture of beer and sak6. Numerous yeast organisms are active 

 in wine, cider and in other fruit juice fermentations. The student desiring 

 further information is referred to the works by Hansen and Jorgensen, 

 which may be found in any library of scientific books. Cider vinegar and 

 yeast manufacture have been mentioned elsewhere, hkewise cheese 

 making and the significance of dairying organisms in the ripening of 

 cream and of butter, etc. 



D. Acid Forming Ferments 



As is known, dilute alcohol upon standing exposed to air, gra,dually 

 becomes sour, losing its alcohol more and more. This is due to ferments 

 which act upon the alcohol, splitting it into acetic acid and H2O. The 

 organisms producing the acid forming enzyme are generally classed with 

 the bacteria, largely in the group Bacillus, the principal species being 

 Mycoderma {Bacillus) aceti, B. pasleurianum, B. kutzingianum, B. 

 oxydans, and B. acetosum. The yeast Saccharomyces mycoderma is also 

 capable of forming acetic acid. The vinegar organisms are most active 

 at 25° to 30° C. Very slowly active at 10° C. and killed at temperature 

 but slightly above 35° C. The so-called mother of vinegar consists of 

 an agglutinated mass of vinegar organisms and is used as a starter in the 

 manufacture of vinegar. Thus far it has not been possible to isolate the 

 vinegar ferment as has been done with diastase and zymase. 



There are acids of non-alcoholic origin formed by living ferments, such 

 as oxahc acid, maUc acid, citric acid and others, which appear to be de- 

 rived from sugars direct. Citric acid is formed from sugars through the 

 activity of two fungi, Citromyces pfeferianus and C. glaber. Saccharo- 

 myces hansenil forms oxalic acid from mannit and galactose, without 

 alcohol formation. 



The following table will serve to make clear the relationship of the 

 diastase (starch), zymase (sugar) and alcohol ferments: 



Principal foods for enzymes 



Starches and 

 dextrins 



Sugars 



Alcohol 



Enzymes . 



Principal Products. 



Diastases 



Sugars 



Zymases 

 (yeasts) 



Alcohol 



Vinegar 



ferments 



(Mycoderma) 



Acetic Acid 



