66 THE ROYAL SOCIETY OF CANADA 



MacConkey's N.R.B. Broth + Lactose: 24 hours, 37°C. No re- 

 duction, gas, slimy. In 72 hours no reduction to canary 

 yellow. 



Agar Colonies: 18 hours, 37°C. growth rapid and abundant, 

 surface colonies average diameter 2 mm., many up to 3 mm. 

 diameter; round, glistening, iridiscent, convex; by trans- 

 mitted light creamy white to dark white at centre, merging 

 to porcelain white to bluish transparency at edges. Under 

 low power objective edges entire, immediate centre dark, 

 remainder of colony lemon colour, becoming paler towards 

 edges, structure finely granular. Subsurface colonies to the 

 eye are punctiform to 1 mm. diam.; under the low power 

 objective, colonies round or eliptical ; edges entire varying to 

 jagged excrescences; structure "mound like", too dense for 

 dififerentiation. 



In 40 hours some surface colonies increase to 6 mm. 

 diameter, and are distinctly iridiscent. 



Colonies are very slimy, the greatest difficulty being 

 experienced in separation from the needle. On placing the 

 platinum loop to large surface colonies fine threads approxi- 

 mating to 15 cms. are drawn out from the plate. 



Gelatine Colonies: Room temperature 48 hours (1st appearance). 

 Surface colonies -5 mm. diam., round, white to bluish-white 

 by transmitted light. Under the low-power objective 

 colonies are lemon to light brown in colour, structure gru- 

 mose, edges irregular, in seom cases fringed. Sub-surface 

 colonies very similar, but granular to grumose, in structure. 



Temperature Relations : 



Thermal Death Point: 10 minutes exposure in nutrient broth 

 at 60°C. 



Optimum Temperature: On beef peptone agar at 37°C. growth 

 luxuriant; at room temperature growth moderate; at 15°C. 

 growth scant., in 20 hours respectively. At the lower 

 temperatures growth moderate to luxuriant in 48 hours. 



In milk a decided preference is shown for 37°C., See 

 page 65; at room temperature sliminess is barely perceptible 

 in 48 hours, coagulation being delayed for several days; 

 at 14°C. sliminess is but slight after 11 days and coagulation 

 is just beginning. Hence the most suitable temperature 

 for growth is 37°C. 



