PRESERVING FOOD 73 



which when strong enough to hinder the growth of 

 bacteria are thought to interfere more or less with the 

 digestive processes of man. The use of any such sub- 

 stance is prohibited by the U. S. pure food law. 



It would seem that eggs at least should be free from Clean 

 bacteria because of their enclosing shells. But experi- Eee * 

 ments have shown that the newly-laid egg is sometimes 

 infested with bacteria and their growth may bring 

 about the decomposition of the egg. 



The more common danger, however, is that of un- 

 clean conditions of nest or storage. The shell is porous 

 to air and also, it has been found, to certain bacteria. 

 The shells, then, should be clean. Eggs are often pre- 

 served by a coating of shellac or in lime water. These 

 methods exclude air, without which any germ inside 

 cannot grow, and they prevent any germ on the out- 

 side from passing through the shell. 



We see, then, why eggs should be kept in a clean, 

 cool place, and if packed, the packing boxes or material 

 should be clean. Eggs are often tainted by moldy 

 packing boxes, sour hay, or dirty straw. 



Some of the less common acts of bacteria are inter- 

 esting even if we suffer by them. 



Fig. 49 shows a plate which was placed on the out- Dust Garden 

 side sill of a second-story window on the back of a city olt^f Doors 

 house. This window overlooked an open field border- 

 ing on a large body of water. It was not, therefore, 

 an especially dusty position and the day was quiet, with 

 little wind. The fact that so many dust-plants were 



