BACTBKIOLOGICAL ASPECTS OF DEHYDRATION 115 



Working with bacteria, Zopf found that Bad. vernicosum would 

 produce fermentation of 70 per cent sucrose in a mixture 

 with cottonseed meal, and that Staphylococcus aureus destroyed 

 cane sugar gelatin in a concentration of 48 per cent. 



Grafenhan showed that certain bacteria will grow on 70 per 

 cent cane sugar and dextrine. 



The Kopeloffs, again, have confirmed or even exceeded these 

 figures. 



It is interesting to note on this point that cane sugar, or sugars, 

 have generally been the subject which have been used for tests. 



Although bacteria generally tend to disappear or at least to 

 become inactive when the moisture falls below 40 per cent, there 

 are many instances known when percentages of water much 

 smaller than this will still permit growth. The ordinary evap- 

 orated fruits, such as apples, peaches and apricots contain in 

 general about 20 to 24 per cent moisture. While usually this 

 high concentration is sufficient to inhibit development, it some- 

 times requires but a small addition of moisture to permit growth 

 and consequent deterioration by molds and yeasts or their en- 

 zymes. It must especially be borne in mind that the enzymes of 

 these microorganisms, as Kopeloff has quantitatively proved, may 

 be active even in the presence of minute moisture percentages, 

 and that they may bring about marked deteriorations. This 

 we have also found to be true in certain dehydrated products. 



Resistance to drying and ability to increase in the presence of 

 small percentages of water seems to be particularly characteristic 

 of soil bacteria and those native to vegetables themselves while 

 most microorganisms of pathogenic character, accustomed to the 

 fluids of the body have fortunately much less endurance to dry- 

 ness. The importance of this fact (if it proves to be a fact) in 

 the preparation of dehydrated food substances cannot be over- 

 estimated. 



BACTERIOLOGY OF DEHYDRATED VEGETABLES 



It was my good fortune, during the period of the war, when I 

 was in the Food Division of the Surgeon General's Office, to have 

 assigned to me a certain part of the investigation work on new 



