174 FERMENTATION IN MILK 



(2.) Red Milk 



The peculiar red coloration sometimes apparent in milk can 

 be traced to several causes, two species of the sarcina group 

 amongst others possessing this property, which is equally shared 

 under certain climatic conditions by the Bacillus prodigiosus} 

 although in this latter case it is the surface only on which the red 

 coloration takes place. 



It is of importance clearly to differentiate between milk 

 reddened by the admixture of blood from the mammary gland, and 

 that produced by the organism isolated and studied by Hueppe 

 and Grotenfeld — Bacillus lactis erythrogenes — the presence of which 

 in the milk is now looked upon as the active causation of the disease. 

 In the former case the coloration is apparent immediately after milk- 

 ing, is uniform, and if the milk is allowed to rest the flocculent blood 

 coagulum causing the coloration will gradually sink and deposit 

 itself in the form of a precipitate at the bottom of the milk recep- 

 tacle. In the latter the red spots do not appear until later, the 

 infection of the milk is comparatively slow, and the milk serum 

 is alone affected, the cream layer not taking the red coloration. 

 This is probably due to the simple fact that the cream layer being 

 on the surface is exposed to the light, which inhibits the colora- 

 tion. A general coagulation of the milk takes place accompanied 

 by a distinctive sickly sweetish odour. The red coloration will 

 not take place if the milk is exposed to light or has an acid 

 reaction. 



The Bacillus lactis erythrogenes of Hueppe {Bacterium erytJiro- 

 genes of Grotenfeld) is an aerobic, liquefying, non-motile, non- 

 sporing, chromogenic bacillus of i to 1-5 mm. in length by -3 

 to -4 mm. in breadth, at times attaining, especially in broth 

 cultures, a length of 4 to 5 mm. in the form of filaments. It takes 

 readily all ordinary stains and holds the Gram. In sterile milk a 

 gradual precipitation of the casein takes place with a neutral or 

 slightly alkaline reaction of the medium. The resultant serum, in 

 the absence of light, absorbs the red colouring matter produced by 

 the organisms, taking a deep red tint provided the medium has no 

 acid reaction. The coagulation by rennet of milk infected with 

 the organism has the effect of producing a marked dirty red 

 coloration, changing to a reddish-brown and finally to blood 

 red. 



The organism produces no red coloration in the presence of 

 * According to Hueppe " mostly B. prodigiosus — rarely by Sarcinas." 



