310 AGRICULTURAL BACTERIOLOGY. 



readily passed by bacteria, and thick-skinned fruits are in 

 a measure protected from decay. Hence it follows, also, 

 that the person who is desirous of preserving fruit must take 

 especial pains to keep the skin from injuries and bruises, for 

 through such wounds in the skin the bacteria find most ready 

 entrance, and once within the softer parts they produce rapid 

 decay. Hence, too, we see why one decaying piece of fruit 

 will contaminate its neighbor, inasmuch as it will furnish a 

 center of active bacteria, which multiply and become so nu- 

 merous as to be sure to pass from one fruit to another. In 

 these facts too do we find the explanation of the increased 

 period of preservation which the fruit dealer can give to his 

 fruit by careful wiping and cleaning it at intervals, since this 

 removes many of the bacteria which would otherwise be likely 

 to find a means of getting through the skin. In short, the 

 whole secret of keeping fruit finds ready explanation when we 

 bear in mind that the putrefactive bacteria, although abundant, 

 do not with readiness pass through the fruit skin, and, conse- 

 quently, that any means which keeps the skin intact and clean 

 will delay the entrance of bacteria and hence the decay of the 

 fruit. But in spite of the best of care their entrance cannot be 

 wholly prevented, for some point of rupture in the skin will 

 surely be found and all fruit is certain to undergo decay in time. 

 To preserve fruit for any length of time it is necessary to 

 adopt more efficient means. 



DRYING. 



The most easily applied means of preventing the growth ot 

 bacteria in food products is by more or less completely drying 

 them. Bacteria demand considerable water and will not grow 

 unless well supplied. They must all grow in a medium that 

 is practically liquid, inasmuch as they are able to absorb food 

 only in a liquid condition. Most bacteria will cease to grow 

 when the amount of water falls to 30 per cent, and all stop 



