80 DAIRY BACTERIOLOGY 



heating process, but which is surrounded by cooling water instead 

 of by steam. If the milk sterilised in this way is filled into 

 sterilised cans, avoiding infection from the air (Jonas Nielsen has 

 patented special appliances for this purpose), it may be sent any 

 distance. On passing through Jonas Nielsen's steriliser the milk 

 undergoes a partial homogenisation. Milk and cream intended 

 for export should, in order to meet all eventualities, be sent as 

 cold as possible, and in this connection it may be mentioned that 

 the results of cooling are in general far more noticeable in heated 

 than in raw milk (provided only that the milk vessel has not been 



FIG. 56. Jonas Nielsen's Steriliser. 



contaminated or rinsed with unboiled water), for the bacteria 

 which grow best at low temperatures are the first to be destroyed 

 on heating while the most resistant spores only germinate at high 

 temperatures. In the production -of sterilised cream (export 

 cream) homogenisation also plays a very important part, as cream 

 with a certain fat percentage appears to be richer the more finely 

 divided the fat globules. Cream, however, like condensed milk, 

 cannot be homogenised at quite so high a pressure (at the most 

 150 atmospheres) as ordinary milk which may be treated right up 

 to 250 atmospheres. 



If the object is only to free the milk from pathogenic germs, and 

 to increase its keeping powers to some extent, complete sterilisa- 



