262 BACTERIA IN MILK AND THEIR SOURCES 



the milk, if kept for several weeks, is left in an almost 

 sterile condition, or containing only moulds and similar 

 fungi capable of tolerating the acidity of the medium. 



Ex. 132. Take about 250 to 300 c.c. of milk at the cowshed, 

 and after thorough mixing pour 50 to 60 c.c. into four small 

 flasks ; label them Nos. i, 2, 3, and 4 respectively. 



Keep No. i cool with ice. \ 



2 at a temperature of 10 to 1=5 C. 



o n Mor 6 hours. 

 3 20 to 25 C. 



4 35 C. J 



After this, determine the number of bacteria per c.c. in each 

 of the four samples by method described in Ex. 125. 



Ex. 133. Determine the numbers of bacteria in a sample of 

 milk taken at the farm into a sterile flask as soon as possible 

 after being drawn ; then, at the following intervals, using both 

 agar and gelatine media for the work : 

 2, 4, 6, 12, 24 hours. 

 4, 8, 12, 24, 40, 80, 120 days. 



The milk to be kept all the time in a tightly-corked flask at 

 ordinary room temperature. 



Note the appearance of mould colonies on the plates inocu- 

 lated with the older milk. 



3. Methods of reducing the Numbers of Bacteria 

 in Milk. To obtain a supply of milk with the least 

 possible number of bacteria in it, necessitates constant 

 attention to cleanliness on the part of all concerned in 

 its production and distribution, and the maintenance of 

 low temperatures so that the organisms unavoidably 

 present in it cannot multiply to an objectionable 

 extent. 



It is not within the region of practical dairy farming 

 to obtain a commercial supply of milk absolutely free 



