HEAT 179 



in some liquid in which bacterial growth can not take place, 

 but the liquid must be of such a nature that it will not be 

 absorbed by the eggs. For this purpose sodium silicate, 

 or water-ylasx, is most frequently employed. The colloidal 

 nature of this silicate prevents its passage into the egg, and 

 the alkalinity of the solution stops all bacterial growth. 

 No desiccation can, of course, take place. If the eggs have 

 been invaded by bacteria before placing them in the water- 

 glass, the growth of the bacteria will not be inhibited. In 

 such cases, gaseous by-products may be formed in the egg 

 to such an cxtcni ihal rupture of the shell occurs, in which 

 case the ill-smelling decomposition products will be ab- 

 sorbed by the remaining eggs to such a degree as to injure 

 their commercial value. The best practice is to place the 

 - in \viitT-rliiss the same day they are laid. 



Preservation by heat. Virtually the only way by which 

 the microorganisms present in any food can be completely 

 destroyed is by the application of heat. The vegetative 

 cells of bacteria, yeasts, and molds are easily destroyed 

 when subjected to temperatures approximating 140- 

 150 F. The spore stages of all types are more resistant, 

 but particularly so with the bacteria that require a tem- 

 perature exceeding that of the boiling-point before they 

 can be completely destroyed. It is therefore easy to free 

 any food substance from all organisms except the spores 

 of bacteria. 



In practice two processes are used : first, the application 

 of a temperature slightly exceeding the scalding-point of 

 water, from 140 to 165 F. This process, known as pas- 

 tciirization, from the fact that it was first employed by 

 Louis Pasteur in the treatment of wines to prevent ab- 

 normal changes, does not destroy all microorganisms, but 

 only those in the vegetative or growing stage. The more 

 effective process, known as sterilization, utilizes tempera- 



