150 CHROMOPAROUS BACTERIA. 



house of a farmer. The blue coloration appears from twenty-four 

 to seventy- two hours after the milk is drawn from the cow, the 

 process being accelerated by warm, close weather, and retarded by 

 cold. At a temperature of i5-2o R. (i8J-25 C.), it may ensue 

 in twenty hours the shortest limit of time observed by H. 

 whilst, at only a few degrees above zero, it may linger on to the 

 seventh day. The coloration always begins to form at the surface, 

 never in the depths of the liquid, and generally appears at first 

 as isolated patches or dots, immovable, and increasing in circum- 

 ference and depth ; so that there are various stages, ranging from 

 single superficial patches to almost complete impregnation of the 

 mass with blue colour." 



F. NEELSEN (I.), in 1880, took up the work commenced by 

 Fuchs. Convenient and reliable methods of pure cultivation were, 

 however, lacking at that time, and, in fact, the cultures prepared 

 by ]STeelsen, when subsequently examined analytically at the 

 laboratory of the Eerlin State Board of Health, were found to 

 consist of a mixture of four species of bacteria, only one of which 

 proved capable of developing blue coloration in milk. This one 

 was named by HUEPPE (IV.) Bacillus lactis cyanogenus, and consists 

 of actively motile, spore-producing rods, 0.3-0.5 /z broad, 1-4 p, 

 long, such as are shown photographically in Fig. III. of Plate I. 

 They are non-liquef active towards gelatin, and are extremely 

 sensitive to higher degrees of acidity in the medium, a circum- 

 stance explaining the facts (noted by Haubner) that sour milk 

 does not turn blue, and that blue patches produced in sweet milk 

 cease to spread when the latter turns sour. 



This fission fungus is highly aerobic, and consequently requires 

 oxygen as an essential factor for its development. In order that 

 this need may be supplied, the organism always grows on the 

 surface of the liquid, so that the colour is produced in that situa- 

 tion solely, and only becomes disseminated through the bulk of 

 the milk by diffusion. 



This microbe grows not only on milk (and equally well on 

 human milk as on that of the cow, ewe, goat, mare, ass, and dog), 

 but also on many other media. On several of these (e.g. almond 

 milk, boiled rice, boiled potatoes, vegetable casein, Cohn's nutrient 

 solution qualified with ammonium lactate) it also develops colour- 

 ing matter which, on the other hand, is not formed in cultures 

 on animal albumin (egg-albumin, blood serum), gum, and a few 

 other media. In artificial inoculations the period of incubation, 

 i.e. the time elapsing between the inoculation and the visible 

 appearance of the blue coloration, is found to be about twenty 

 hours, but, as Haubner ascertained, depends on the prevailing 

 temperature. Milk with a tendency to this disease transmits the 

 property to the butter prepared from it. 



The colouring matter is not stored up within the cell, but is 

 merely produced there and excreted into the surrounding medium; 



