DEVELOPMENT OF COLOUR IN MILK 281 



the liquid is rendered very ropy, the slimy product being the 

 gummy carbohydrate dextran. 



(ti) An organism very closely resembling Str. lacticus was found 

 by Burri to be the cause of slimy milk and whey in a Swiss dairy. 

 He traced it to the milk ducts in the udder of some of the 

 cows. 



3. Development of Colour in Milk. Many bacteria 

 possess the power of manufacturing colouring matter, 

 which may become distributed in the media in which 

 they are growing, colouring them red, pink, yellow, blue, 

 or some other tint. They may occur in milk, although 

 colour production through the agency of bacteria is 

 rarely met with in this liquid, and then only when it is 

 kept a considerable time. The following varieties of 

 coloured milk are best known : 



(i) Red Milk. It is not very uncommon to meet 

 with milk having a reddish tinge or which deposits a 

 reddish sediment after standing for a time in a can or 

 other Vessel. The colour is due to the presence of 

 blood derived usually from the rupture of a small blood- 

 vessel in the udder of the animal. In such cases the red 

 blood corpuscles are readily detected by the microscope 

 (see p. 302). In some instances, however, the red colour 

 is not visible in the milk freshly drawn, but develops 

 slowly and increases slightly from day to day. Such 

 examples are. due to the growth of certain species ot 

 bacteria, of which the following have been isolated and 

 studied : 



(a) Bacterium erythrogenes, L. & N. (Bacillus lactis 

 eryihrogenes, Grotenfelt). The organism is non-motile and rod- 

 shaped, .8 to 2 /& long and .5 to .8 /a thick. When grown in 

 milk its coagulation occurs slowly, the serum separates from the 



