162 Microbes and You 



are dried. Thick materials like pus or sputum will retard drying 

 and exert a protective effect on the organisms. (2) Drying films 

 in the light is more destructive to bacteria than is drying in the 

 dark. (3) The higher the drying temperature, the more destruc- 

 tive to living cells. (4) Drying in air is more lethal than desiccation 

 in a vacuum or in a gaseous atmosphere like inert nitrogen. (5) 

 The nature of the organism, whether it be a spore-former or just 

 a resistant form like some cocci, directly affects resistance to drying. 

 Complete desiccation seems to suspend bacterial action, and in time 

 the cells perish. The drying of foods as a means of preservation is 

 predicated upon the need of moisture for microbial activitv. 

 Deprive a bacterium of water for a long enough period and the 

 organism will usually not be a factor in the spoilage of food as 

 long as the moisture level is kept below a certain point. There is 

 some evidence, however, that the enzymes of organisms may con- 

 tinue to act even in the absence of bacterial growth. 



People have dried meats and fish for centuries as a means of 

 preservation, but they didn't know the bacteriological laws under- 

 Iving the success of their methods. Such foods as dried figs, dried 

 apples, prunes (dried plums), and raisins (dried grapes) keep 

 well because of a combination of physical changes. As moisture 

 is removed, the relative concentrations of sugar go up, and this in- 

 creased sugar concentration adds to the unfavorable conditions for 

 bacterial growth as we shall see in the discussion of osmosis. 



The possibilities of dehydration were given adequate field 

 trials during World War II, as many GI's will attest. Entire meals 

 of so-called reconstituted foods were quite common. Dehvdrated 

 milk, eggs, potatoes, etc., were used in tremendous quantities for 

 feeding the troops. The space and the weight conserved by de- 

 hydration are considerable, and during time of war, such factors 

 are of paramount importance. Why ship heavy, bulky water to 

 far-flung areas where water is readily available? It is like carrying 

 coals to Newcastle. While the principles of dehydration are sound, 

 a steady diet of dried powder and a glass of water can become 

 very tiring, even though it mav be nutritious. 



Drying may not kill some bacteria, and upon hydrating de- 



