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 
bacteria because of their enclosing shells. But experi¬ 
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¬ 
side sill of a second-story window on the back of a city 
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 
Clean 
Eggs 
Dust Garden 
Planted 
Out of Doors 
