THE EELATION OF MICROORGANISMS TO MILK 367 



been kept. Such milk may also contain large numbers of those sapro- 

 phytic organisms which occur in the atmosphere and about the stables 

 and milk-house. The number of this group depends largely upon the 

 sanitary conditions of production and the initial contamination. In 

 ordinary milk organisms of the Bad. lactis acidi type will constitute a 

 very large percentage of those present when the milk reaches the city 

 even before it shows any perceptible signs of souring. During the past 

 few years great progress has been made in the production of clean milk, 

 and at present quite an important part of the general milk supply of our 

 cities has a very much lower germ content than it had a few years ago. 



Special Milks. — In this class may be considered those milks known 

 as Selected, Inspected, or Guaranteed. As commonly used these terms 

 mean milk which has been produced and handled with considerably 

 more care than ordinary market milk but not with the extreme care 

 required for certified milk. Guaranteed milk is produced by herds 

 which have been shown by the tuberculin test to be free from tubercu- 

 losis. Considerable care is exercised in aU the operations of handling 

 the milk. The result is that these milks usually have a much lower 

 germ content than the ordinary milk supply of the same city. Some- 

 times the germ content of such milk compares favorably with that of 

 .certified milk. These milks may contain various types of normal milk 

 organisms but they should not contain any tubercle bacteria. 



Certified Milk. — Certified milk means milk which has been pro- 

 duced according to the regulations of and under the supervision of a 

 medical milk commission. The stables and cows are kept extremely 

 clean. No dust is allowed in the stable at milking time. The cow's 

 flanks and udder are washed just before milking, the milkers wear white 

 suits and wash their hands before milkjng each cow. Small-top pails 

 are used and the milk is cooled as soon as drawn from the cow. The 

 extreme care exercised in the production and handling of this milk has 

 a very marked efEect on the number of bacteria found in it. The follow- 

 ing counts are typical of certified milk. 



