BUREAU OF ANIMAL INDUSTRY. 239 



terial content of the milk, the efficiency of the pasteurization, and the 

 handling of the milk after pasteurization. There ^vas observed no 

 development of bacteria in the pasteurized milk that could be said 

 to make it more unsafe than raw milk kept under similar conditions. 

 This work has been completed, and a full report of it is now in the 

 hands of the printer. 



An exhaustive investigation is now under way for the purpose of 

 determining the number and variety of bacteria that survive pasteur- 

 ization under controlled conditions. 



The alkali-forming bacteria which cause the decomposition of milk 

 play a very important part in market milk, and particularly in clean 

 raw milk and pasteurized milk. Dirty milk sours quickly, and hence 

 is discarded by the ordinary consumer before the alkali formers have 

 had time to develop and decompose it, but such is often not the case 

 with clean milk. A knowledge of the thermal death point of this 

 class of bacteria is therefore very important, and a study of this sub- 

 ject is being made. 



For several years the Dairy Division has been cooperating with the 

 Missouri Experiment Station in conducting experiments pertaining 

 to milk secretion. The main problem under investigation is the effect 

 of feed on the composition and properties of milk. Before it was 

 possible to study this problem, however, it was necessary to investi- 

 gate many minor problems that had an important bearing on the main 

 problem, such as, for example, the normal variation in milk from 

 milking to milking, the variation occurring during the advance of 

 the lactation period, the variation due to the cows gaining or losing 

 in body weight, the variation due to different breeds, etc. Some of 

 these experiments have been completed and the results published; 

 others are almost completed. The work in progress or recently 

 completed is as follows : 



1. The effect upon the milk of gaining or losing body weight. The 

 cows are fed so that they will gain or lose in weight, and the composi- 

 tion of the milk is studied. 



2. The effect of cotton seed, cotton-seed meal, and cotton-seed hulls 

 on the composition and properties of the milk. This investigation 

 is not complete, but so far there is less effect from such feeds than is 

 usually attributed to them. 



.3. The changes in milk from milking to milking. Comparisons are 

 made between earlier and later portions of the same milking, also 

 between milk drawn twice, three times, and four times a day. The 

 data are practically complete. 



4. The composition of human milk and changes during lactation 

 period, as compared with cow's milk. The investigations are com- 

 pleted, but not ready for publication. 



5. Some progress has been made in isolating and identifying the 

 coloring matter of butter fat. 



f). A method and an apparatus have been devised for measuring the 

 hardness of butter fat and other fats. The methods previously in use 

 were crude. The new method promises decided improvement. 



CHKESE INVESTIGATIONS. 



Swiss cheese. — The investigations at Albert Lea. INIinn., relative 

 to various problems involved in the manufacture of tiie Swiss type 

 of cheese, have been continued. Most of this work has been prelimi- 



