E. M. Doidge 23 



circumference and, when examined microscopically, are granular in 

 texture. The submerged colonies are minute, irregular in form and 

 granular (Plate XI, fig. a). 



After 48 hours the colonies are 1—2 cm. in diameter, rather irregular 

 in form and with a lobate margin. There is a dense spot in the centre 

 surrounded by one or two concentric rings. The colour is white by 

 reflected light, and a coppery tint by transmitted light. The colonies 

 do not increase in size after this, but change somewhat in colour and 

 texture up to the fifth day ; at this time the colour is maize yellow or 

 buff yellow (IV, VO — Y,f—d) and the colony is surrounded by rather 

 a heavy margin (Plate XI, fig. a) ; the surface is smooth and shining, 

 and slightly raised. 



In thickly sown plates the colonies are irregularly circular, with a 

 less deeply lobed or almost smooth margin. 



At 30° C. the form of the colonies is somewhat different; they attain 

 a diameter of 1 — 5 mm. in 24 hours. They are opalescent by trans- 

 mitted light, with some concentric rings, finally becoming yellow as at 

 25° C. The maximum diameter is 6 — 10 mm. and the colonies are 

 irregularly circular with a heavy margin. 



At 37°C. growth is also rapid, the colonies are more opalescent than 

 at 30°C. and the concentric rings are more conspicuous. When mature, 

 the colonies are circular and the margin smooth ; the colour is slightly 

 deeper than at the lower temperature. The centre of the colony is very 

 slightly raised, and in some there is a heavier ring about 1 — 2 mm. from 

 the edge, with radiations towards the margin. 



The growth at 20° C. is comparatively slow. Colonies are only just 

 visible to the naked eye after 24 hours when they, consist of a dense 

 white spot surrounded by a translucent margin. At this temperature 

 thin, spreading colonies are finally formed 7 — 8 mm. in diameter. They 

 are irregular in shape, and no definite yellow colour is developed ; the 

 colonies remaining a creamy tint (19 yo — y). 



In old plate cultures, especially those at the higher temperatures, 

 there are numerous X -shaped crystals formed (Plate XI, fig. b). In all 

 young cultures when examined microscopically, a swaying movement is 

 noticeable right through the colony, due to the activity of the rods 

 composing it. 



Nutrient agar streak. On nutrient agar with a reaction of + 15 Fuller, 

 there is quite a plentiful growth after 24 hours at 30° C. It takes the 

 form of a glistening homogeneous streak along the needle track which is 

 somewhat opalescent by transmitted light, milky white by reflected light. 



