868 THE BACTERIAL ORIGIN OF MACROZAMIA GUM 



when the cultural characters were examined as when the organism 

 was isolated. Microscopically, the colony consists of a central 

 grey-brown and rather opaque area and a transparent margin. 

 The outer portions of the central area are sometimes mottled 

 and sometimes consist of radiating filaments. The transparent 

 margin has a lacerate-erose edge which becomes smooth, while 

 the broad zonate margin becomes tinged with brown and trans- 

 lucent. The deep colonies are rounded and opaque. 



Nutrient agar plate. — The colonies are circular, raised, glisten- 

 ing and translucent white. A zonate or slightly nipple-shaped 

 appearance is given by the centre being raised above and whiter 

 than the broad margin. Microscopically, the colonies are 

 brownish and circular, with a darker brown granular centre. 

 Occasionally the central granules are placed radially. The deep 

 colonies are rounded or lenticular and either wholly granular or 

 with a granular centre. 



Glucose-gelatine stroke. — The growth is narrow, raised, white- 

 glistening, and has an erose margin that becomes lobular. The 

 stroke remains narrow and the medium is not liquefied. 



Glucose-gelatine stab. — The needle-track develops a rough, 

 white growth. The nail-head spreads out as a thin, slightly 

 undulating, white film with a lacerate-erose margin. It becomes 

 flat, smooth and slightly depressed, but the medium shows no 

 signs of liquefaction. Gas-bubbles are produced in the gelatine. 



Nutrient agar stroke. — A broad, raised, translucent white 

 growth with a slightly erose margin and spreading base is formed. 

 The condensed water carries a film. 



Saccharose-potato-agar. — A raised white slime is produced and 

 the medium is cleft in all directions from the formation of gas. 



Potato.— A dry, dirty-white, flat, glistening growth is formed 

 and the medium is darkened locally. 



Bouillon. — The medium becomes turbid and carries floating, 

 broken films. The sediment is loose. The indol reaction is 

 obtained and nitrates are reduced to nitrites. 



Milk. — The medium appears to thicken, and the reaction 

 becomes strongly acid to litmus-paper. 



