t 754 ] 



the fresh milk by applying to it centrifugal force, and after- 

 wards boiling it to coagulate the albumen and reducing it to 

 a third or fourth of its original volume. It is then poured into 

 metal vessels which are filled and then soldered and then 

 placed at a temperature of 120 C for two hours. The keep- 

 ing quality of the milk is then proved by storing it in a tem- 

 perature of nearly 40 C for a few weeks, after which if the 

 top or the bottom of the vessel distends, it is inferred that 

 gases due to putrefaction have generated inside the vessel, 

 and any vessel showing such distention is rejected. 



(9). Pasteurised milk. By Pasteurising is meant destroy- 

 ing vegetative microbes by continuous heating for a quarter of 

 an hour at a temperature of 75 C, and then sealing up the 

 glass flask containing the milk. This operation makes milk 

 practically safe for use, as the microbes of tuberculosis, typhus 

 and cholera, have no persistent spores capable of resisting 

 great heat, and the milk keeps longer, say for 24 hours, after 

 it has been pasteurised. Pasteurised milk is only temporarily 

 sterilized milk. The safest thing to use, however, is perfectly 

 sterilized milk, or sterilized condensed milk. 



CHAPTER CXXVII. 



DAIRY BACTERIOLOGY. 



TT AV1NG given a general notion regarding the utility of a 

 knowledge of bacteriology, we will now go on with the 

 consideration of certain sp ecial microbes with which agricultur- 

 ists are concerned. Ordinary fresh milk may contain as many 

 as 50 million microbes per pint without looking or tasting any 

 the worse for it. But if the cows and the cowhouse are kept 

 scrupulously clean and if the person milking washes his 



