232 Agricultural Bacteriology. 



germinate on account of the acid reaction of the toma- 

 toes. Corn, peas and nonacid vegetables must be made 

 absolutely free from all organisms. This is often quite 

 a difficult process in the household, hence these are han- 

 dled with less success than are the acid vegetables like 

 tomatoes. 



Preservation by cold. In the modern methods of 

 food preservation, low temperatures are constantly em- 

 ployed. All kinds of foods are placed in cold storage. 

 If the temperature is above the freezing point as must 

 be used with certain kinds of foods, the bacteria grow 

 slowly. If the material is such that the temperature can 

 be reduced below the freezing point, the growth of bac- 

 teria will be prevented. Butter and meats are stored at 

 temperatures far below the freezing point. Eggs and 

 fruits must be kept above freezing. 



Preservation of eggs. Fresh eggs soon deteriorate 

 in quality due to the growth of organisms that cause the 

 egg to spoil. Infection of the egg may occur in the ovi- 

 duct of the hen before the shell is developed. Also, owing 

 to the porous nature of the shell, bacteria may work their 

 way through it into the white of the egg which affords 

 them an excellent food medium. A number of methods 

 have been devised whereby the keeping qualities may be 

 enhanced. These methods are of much practical value 

 as they enable the surplus eggs of summer to be held and 

 disposed of at more profitable prices in winter when fresh 

 eggs are scarce. 



The first step in all processes of preservation should be 

 to keep the eggs clean by maintaining clean straw or 

 other material in the nests. The most successful way of 

 keeping the eggs is by placing them in a solution of water 

 glass (sodium silicate). This compound can be procured 



