BACTERIA OF PUTREFACTION. 149 



that cause decay and putrefaction of various kinds. They 

 cause our richer foods to " spoil/' milk to turn sour, butter to 

 become rancid, etc. 



While these bacteria do not cause disease in the human 

 body, they often make food poisonous. The cases frequently 

 reported of poisoning from eating ice-cream, cheese, sausage, 

 etc., are in many cases due to bacteria in them. We should, 

 in the first place, be careful to get good, fresh foodstuffs. In 

 the second place, it should be so kept as to prevent the intro- 

 duction and development of bacteria in them. Bacteria need 

 heat for their growth (as we so well know is the case with 

 the higher plants). They also need moisture. 



So our principal modes of keeping foods from spoiling are 

 to keep them in a cold place, or to dry them. Or we heat 

 them, and then shut them away from the air, as in our various 

 modes of canning and preserving foods. Salting and smoking 

 meats, etc., preserve them by preventing the growth of bac- 

 teria. Cold does not usually kill bacteria. So, milk that has 

 been kept in a refrigerator, and that seems sweet, may have 

 in it a stock of bacteria that develop after we drink the milk, 

 from the heat of our bodies. There are now known ways of 

 killing the bacteria in milk and other liquids, known as "ster- 

 ilizing," that make us safe from this"danger. 



When we awaken on a cold winter morning, we are likely 

 to find that the fire in our hard-coal stove has burned low. 

 Not enough heat is given out. What is the trouble ? Is it 

 merely that more coal is needed ? We put another hod of 

 coal in the magazine (though some usually remains). Does 

 this bring the desired result ? No. We open the draft. Is 

 this sufficient ? It is not. We must shake down the grate 

 and clean out the clinkers. The removal of waste is often 

 more necessary than the addition of a fresh supply of mate- 

 rial. It is often a more serious matter to have the waste pipe 



