400 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



eggs in the market is an indication of difference in actual value, and the 

 sale of cold-storage eggs for new-laid or strictly fresh eggs is generally 

 recognized as a fraud by the purchaser and doubtless will in time be so 

 recognized by law. The cold-storage egg is nevertheless a very valuable 

 food and the economic importance of saving the over-abundant supply 

 produced during the spring for use during the colder season of the year 

 makes this industry a great benefaction to the public. Suitable regula- 

 tion may be expected to remove its objectionable features. 



MILK AND BUTTER. Milk as ordinarily sold at retail is not subject 

 to sufficient seasonal change in market price to make its prolonged storage 

 advisable. But milk is so rapidly changed by bacterial activity at ordinary 

 temperatures that efficient dairy methods necessarily include prompt 

 cooling of the milk after it is drawn from the animal, and the maintenance 

 of a low temperature until it is delivered to the consumer. At the low 

 temperature bacteria slowly multiply, unless the milk is actually frozen, 

 but at a temperature slightly above the freezing-point very clean milk 

 may be kept in perfect condition for a week, and it may be kept sweet 

 for several weeks. Refrigeration of milk cannot compensate for un- 

 healthy animals producing it, nor for careless and uncleanly methods of 

 handling. The cold does not destroy the microbes in the milk but only 

 retards their multiplication and chemical activity. In practice, espe- 

 cially in the transportation of milk into large cities it is frequently most 

 economical to freeze the milk and trust to insulation and the latent cold 

 in the ice to maintain a low temperature during transportation. Such 

 milk should arrive at its destination in a partly frozen condition. 



The cold storage of butter is essential even when it is kept for only 

 short periods, and the seasonal variation in price is sufficient to warrant 

 its storage from summer to winter. The keeping qualities of butter 

 depend upon many factors,* and the most efficient cold storage cannot 

 compensate for previous deficiencies. In refrigerated butter there is a 

 gradual diminution in the total number of living bacteria, with possibly 

 a multiplication of a few particular kinds. There is a slow increase in 

 acidity. In frozen butter the bacterial content and the chemical com- 

 position remain practically unchanged. 



FRUITS AND VEGETABLES. These foods are for the most part adapted 

 for preservation for short periods at ordinary temperatures, and cold 

 storage at a temperature slightly above zero is very effective in diminishing 



* See chapter on the microbiology of butter. 



