7O PRACTICAL DAIRY BACTERIOLOGY 



leaves of plants, where he thinks it multiplies naturally. 

 Whether this may be regarded as its natural home cannot yet 

 be stated. It is suggestive to note, however, that when found 

 in fresh milk it does not appear to be in a vigorous condition, 

 and grows much less rapidly than it will after it has been 

 developing in milk for a number of hours. This suggests that 

 whatever be its immediate source in the dairy it does not come 

 from a location especially well adapted to its life. 



Bact. aerogenes and other gas-producing organisms are also 

 from sources external to the cow. They practically never come 

 from the cow's udder, but chiefly from the dirt of the cow or 

 from the faeces, and they may, also, be derived from the air 

 or other external filth contamination. Sometimes they, too, will 

 be found in incompletely sterilized milk vessels. The practical 

 conclusion to be drawn is that the dairyman's method of avoid- 

 ing the troubles arising from gas-producing organisms is the 

 extra care taken to prevent external contamination of the milk, 

 or extra thoroughness in washing vessels. 



B. coli communis. This organism, so far as we know, conies 

 wholly from faecal contamination. It is quite common in milk, 

 as would be expected from the well-known fact that it is a 

 constant inhabitant of the intestine, and that almost all milk 

 is contaminated with manure. Its presence in milk would prove 

 a very serious contamination, if the faecal contamination were 

 from human beings, but inasmuch as it comes from cows the 

 contamination is less serious than it would be from a human 

 source. 



The other types of bacteria found in milk need not especially 

 detain us here. The udder itself furnishes merely harmless 

 germs, at least in cases where the udder is free from all dis- 

 ease. The kinds of bacteria which produce trouble in milk, 

 slimy milk, bitter milk, etc., come from such a miscellaneous 

 variety of places that no definite sources can be named. In 

 cases of trouble each must be traced to its own source, which 



