BACTERIA WITH NO EFFECT ON MILK. 89 



be regarded as dairy infections for they occur under condi- 

 tions of bacteriological experiment only. Quite a number 

 of the bacteria found in milk are capable of producing differ- 

 ent pigments if they have a sufficient time for action. By 

 inoculating tubes of sterilized milk with different species of 

 bacteria we can obtain in the tubes all the colors of the rain- 

 bow, and all by the action of bacteria found in milk. But 

 the bacteria do not grow sufficiently in ordinary milk to 

 produce these effects. None of these types of milk, unless 

 possibly it may be yellow milk, has ever been known to occur 

 as a dairy infection. They are phenomena of interest to 

 bacteriologists, but do not occur in ordinary dairying and 

 we need not, therefore, dwell upon them. 



BACTERIA WITH NO VISIBLE EFFECT ON MILK. 



In addition to the types of bacteria mentioned there is 

 another extremely large group which for the dairyman is of 

 very little importance. It consists of bacteria which have 

 no action upon milk so far as concerns sight, taste or 

 smell. Some of these bacteria apparently do not grow in 

 milk. Others, although they grow rapidly, fail to produce 

 any changes which affect the physical nature of the milk. 

 The milk does not sour or become alkaline, nor does it be- 

 come curdled, even though these bacteria are present and 

 grow in abundance. These bacteria are very abundant in the 

 dairy and in fresh milk. They are found in great numbers 

 in the various forms of contaminating filth in the dairy, and 

 the bacteria that inhabit the milk ducts belong, many of them 

 at least/ to this type. Many species of such bacteria are 

 common in the dairy and sure to find their way in milk. 

 A majority of the bacteria in fresh milk very commonly 

 belong to this type. This group of bacteria, from the 

 dairyman's standpoint, are of little importance. Whether 

 some of them may not be of importance from the stand- 

 point of the wholesomeness of the milk as a food prod- 



