u6 CHROMOPAROUS BACTERIA 



at the laboratory of the Berlin State Board of Health, were found to consist of a 

 mixture of four species of bacteria, only one of which proved capable of develop- 

 ing blue coloration in milk. This one was named by HUEPPE (IV.) Bacittus 

 lactis cyanogenus, and consists of actively motile, spore-producing rods, o. 3- 

 o. 5 /x broad, 1-4 /z long, such as are shown photographically in Fig. III. of Plate I. 

 They are non-liquefactive towards gelatin, and are extremely sensitive to higher 

 degrees of acidity in the medium, a circumstance 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 situation 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 

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

 albumen (egg-albumen, blood serum), gum, and a few other media. In artificial 

 inoculations the period of incubation, i.e., the time elapsing between the in- 

 oculation and the visible appearance of the blue coloration, is found to be about 

 twenty hours, but, as Haubner ascertained, depends on the prevailing tempera- 

 ture. 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 ; Bacillus lactis cyanogenus 

 is therefore chromoparous. The constitution of the colouring matter has not 

 yet been determined with accuracy, but 0. ERDMANN (I.) was led by his com- 

 parative experiments to consideritas one of the aniline group, viz., triphenylrosani- 

 line. Neelsen's endeavours to prepare it in a pure condition were frustrated by 

 reason of its instability. Dilute solutions of acetic acid, hydrochloric acid,"phos- 

 phoric acid, sulphuric acid or nitric acid produce no noticeable alteration. Ammonia 

 gives rise to a violet tint, whilst under the influence of the hydroxide or the car- 

 bonate of potassium or sodium, conversion into a beautiful rose -red occurs, the 

 original colour being restored by acidification. Frequently the low degree of 

 acidity of the milk, under which condition the bacillus is still able to develop, is in- 

 sufficient to enable the colouring matter to assume a deep blue tint. The colour 

 of the surface of the liquid is merely greyish-blue, and only becomes a pure, 

 full blue when the lactic acid bacteria come into action and raise the acidity to 

 a sufficient degree. The colour shade in individual instances may exhibit any 

 intermediate tint between a delicate light blue and the deepest indigo. Accord- 

 ing to Neelsen, the absorption spectrum of this colouring matter, which consists 

 of the strong lines E and F and of a broad band in the yellow, is almost 

 identical with that of triphenylrosaniline. From the researches of C. GESSAED 

 (I.) and K. THUMM (I.), it appears that Bacillus cyanogenus also produces, in 

 addition to the blue colouring matter, a yellow fluorescent substance. L. HEIM 

 (III.) and P. BEHR (I.) have given an account of a variety of this bacillus that 

 had lost its faculty of producing colouring matter in nutrient gelatin, 

 nutrient agar-agar, and skim milk. W. ZANGEMEISTER (I.) found on milk that 

 turned blue spontaneously a fission fungus (B. cyaneo-fluorescens) allied to 

 Bacillus cyanogenus, further particulars of the properties of which will be found 

 in the treatise referred to. 



Bacillus cyanogenus is not injurious to health. The poisonous properties 



