170 OUTLINES OF BACTERIOLOGY 



possibility of multiplication of all the bacteria that are inside that 

 need oxygen, and at the same time prevents others from getting in. 

 The shell is made impervious by immersion in milk of lime, or much 

 better, by the use of water-glass. The latter is a material composed 

 of sodium and potassium silicate. It is cheap, and usually sold in 

 the form of a thick syrup. One part of the syrup is dissolved in 

 ten parts of water, the mixture being poured over the eggs. One 

 gallon of this mixture is sufficient for the preservation of 50 dozen 

 eggs. Eggs can be preserved from decay for several weeks, though 

 indefinite preservation is quite out of the question, because some of 

 the bacteria that are inside the shell, though very much handicapped, 

 yet manage to multiply very slowly, and in course of time induce 

 changes that materially alter the constitution of the egg. 



