CHAPTER IX 



BACTERIA WHICH LIVE UPON DEAD FOOD: 

 SAPROPHYTES 



These include the bacteria found living freely in nature, 

 in the air, in water, and in the soil. Since they live upon 

 dead organic material they may be expected in any kind 

 of food upon which the human being lives, as well as in 

 other substances that do not serve us as food. 



Materials that serve Bacteria as Food 



Some kinds of food are very readily attacked by bac- 

 teria, others with more difficulty, and some hardly at all. 

 Pure sugars are, as a rule,'not attacked by them, although 

 if the sugar is in water solution certain bacteria may some- 

 times feed upon it, and raw sugar is sometimes injured 

 by bacterial growth. The same is true of pure starches, 

 since most bacteria are quite incapable of making use of 

 pure starch. It happens, however, that nearly all of our 

 food materials containing starch and sugar contain also 

 other substances upon which bacteria can feed, so that 

 the sugary and starchy foods in our households are by no 

 means exempt from them. Fats are also attacked by bac- 

 teria, although less readily than some foods. By bacterial 

 action the fat is made rancid and undergoes other less 

 familiar changes. 



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