MILK 205 



more common forms, however, form little acid, and are checked by 

 the growth of the lactic-acid bacteria. 



The bacteria causing bitterness in unheated milk are more fre- 

 quently those of the acid-forming classes, which are better able to 

 compete with the lactic-acid bacteria. The acid formed by this 

 group is usually butyric and not lactic. Some writers have stated 

 that the bitterness is caused directly by the butyric acid. Nearly 

 all of the bacteria known to produce bitterness bring about an active 

 digestion of the casein and albumen, and it is probable that the bitter 

 principle is formed in this decomposition. In most cases, however, 

 the bitterness becomes evident before there is any visible sign of 

 change in the milk. 



Bitter milk may occur as an epidemic, persisting day after day 

 and causing great trouble. This may be due to some constant 

 localized source of infection which adds each day unusual numbers 

 of bacteria to the milk. In some cases it has been found that the 

 udder of a cow was infected. This should be determined by carefully 

 cleaning the udders of all the cows and milking from each quarter 

 of the udder of each cow into fruit jars or bottles which have been 

 previously cleaned with boiling water. 



In case one of these samples shows a well-developed bitterness 

 while others remain normal, it may be assumed that the source of 

 infection is the udder of the cow giving this milk. In that case 

 there should be injected into the udder after each milking a solu- 

 tion of 1 part hyposulphite of soda in 100 parts of water. 



It is probable in many cases that the source of infection is not 

 localized. If through some combination of circumstances the lactic- 

 acid bacteria are suppressed, other kinds become predominant. The 

 utensils, the milk-room, and the stable gradually become inoculated 

 with these bacteria or their spores and each new lot of milk is thor- 

 oughly inoculated. The bitter-milk bacteria may be one of the new 

 forms. In this event it may be necessary, after thoroughly cleaning 

 and steaming everything coming in contact with the milk, to intro- 

 duce some good sour milk from a neighboring dairy. In this way 

 the normal fermentation may be restored and the objectionable 

 bacteria suppressed. 



Ropy or Stringy Milk. In this most troublesome fermenta- 

 tion the milk becomes what is commonly described as ropy or 

 stringy. The milk is slimy and viscid. As this condition increases 

 the milk may be drawn out into threads. 



This fermentation should not be confused with garget, which 

 appears in the fresh milk and is due to an inflammation of the 

 udder. Ropy or stringy milk develops after the milk is drawn and 

 is caused by the growth of certain kinds of bacteria. Although a 

 number of kinds of bacteria causing this trouble have been studied 

 as distinct varieties, it is probable that they are nearly all closely 

 related. They do not form spores and are therefore destroyed by a 

 comparatively low heat. 



If a sample of ropy milk is examined under a microscope it is 

 found to be filled with these small bacteria, each one surrounded 



