94 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



monly in the udder of healthy cows. The pathogenic type may be 

 converted into the fat-splitting type by continued growth on milk. 



The work on the alkali-forming bacteria has been completed by the 

 determination of the source of this group in milk. They come oc- 

 casionally from feces, but more commonly from soil. 



Work of a similar nature has been started on the streptococci oc- 

 curring in milk, and it has already been found that streptococci from 

 pathological sources are differentiated from ordinary milk strepto- 

 cocci by at least one characteristic. 



It has been found that, while there is some variation in the re- 

 sistance of spores of different species of molds, nearly all of them 

 are killed by the usual pasteurizing temperature of 145° F. for 

 30 minutes. 



The most extensive and important work on the bacteria of milk 

 has been the investigation at Beltsville on the sources of bacteria in 

 milk and the effect of various operations on the number and kinds 

 of bacteria found in fresh milk. This work has established that the 

 important factors in producing milk with a low bacteria count are 

 small-top pails, clean udders, and sterile utensils. The excessive 

 numbers of bacteria sometimes found in market milk are due to 

 multiplication rather than to unusually high initial contamination. 



MILK SECRETION. 



Laboratory equipment has been installed and some progress made 

 in a study of the changes in the composition of the blood as influ- 

 enced by the secretion of milk. It has been found that the phos- 

 phorus content of the blood changes as the period of lactation begins. 

 The changes in calcium content were not so definite. 



CONDENSED MILK. 



A 36-inch pan fully equipped for making bulk-condensed milk on 

 a relatively small commercial scale has been installed at the Grove 

 City plant, and is now in successful operation in the making of con- 

 densed skim milk. Although the contract for an experimental con- 

 densery at Washington was placed a year ago, the installation has 

 just been completed. On account of this delay little progress has 

 been made on the experimental work. 



ICE CREAM. 



Considerable attention has been given to the problem of storing 

 fat, and it has been found that butterfat may be separated in a fairly 

 pure condition and stored until needed. This fat remains un- 

 changed, and when emulsified with skim milk can hardly be dis- 

 tinguished from fresh cream in the ice cream. 



CHEESE INVESTIGATIONS. 



Soft cheese. — The work on the soft cheeses has been confined to 

 Roquefort, Cream, Neufchatel, and a soft cheese made from goats' 

 milk. The method of making and ripening cheese of the Roquefort 

 type has been improved until it is highly probable that domestic 

 cheese can be put on the market in successful competition with the 



