NON-PATHOGENIC BACTERIA. 



87 



away from the light. In milk it produces the yellow cream on 

 top of the blood-red serum, or, fluid in the centre, and at the 

 bottom the precipitated casein. 



Growth. Grows rapidly in bouillon and on potatoes ; slower 

 on the other media; Plates. A cup-like depression in the centre 

 of the colony, with a pink coloration around it, the colony itself 

 being slightly yellow. 



Stab Culture. The growth mostly on surface. The gelatine 

 afterwards colored red and liquefied. 



Potato. A golden yellow pigment formed at 37 C., after six 

 days. 



Examination of Milk in Stained Specimen. A drop of milk 

 diluted with a drop of distilled water is dried on the cover-glass 

 and fixed by heat. Chloroform methyl blue, prepared by mix- 

 ing 12 to 15 drops of saturated alcoholic solution of methyl blue 

 with 3 or 4 c.c. of chloroform, is used for staining. The chlo- 

 roform is then evaporated by exposing the specimen for a few 

 minutes to the air. Bacteria blue ; rest of field unstained. 



Another method is to mix a drop of milk with two or three 

 drops of a 1 per cent, solution of sodium carbonate on a cover- 

 glass. Saponification of the fat occurs on heating the mixture 

 to evaporation. The preparation is then stained in the ordinary 

 manner. 



Some Non-Pathogenic Bacteria found in Water. The bacteria 

 found here are very often given to producing pigments or phos- 

 phorescence, and are in great number. The more common ones 

 only will be described. 



Bacillus Violaceus. 



Origin. Water. 



Form. A slender rod with rounded ends, three times as long 

 as it is broad, often in threads ; middle-sized spores. 



Properties. Yery motile ; forms a violet-blue pigment, which 

 is soluble in alcohol, and depends upon oxygen for its growth. 

 Kapidly liquefies gelatine, but not agar. 



Growth. Grows fairly quick, is facultative anaerobic. 



Cultures on Plate. At first the colonies look like inclosed air- 

 bubbles. Low power shows irregular masses, with a centre 

 containing the pigment and a hairy-like periphery. 



