CULTURAL REACTIONS 



377 



and subsequently left in the dark at room temperature. After a variable time 



under suitable conditions, aerial hyphae may develop, 



giving rise to a characteristic bloom on the surface of 



the colony — the chalk powder appearance just described. 

 The anaerobic Wolff-Israel type forms smaller colonies, 



not apparent for 3 or 4 days ; they are more compact, 



greyish or porcelain white in colour, and have a nodular 



surface (Fig. 61). 



On glycerol or glucose agar the aerobic types give 



a luxuriant, confluent, heaped-up, worm-cast, pigmented 



growth, adherent to the medium, of tough consistency, and 



difficult to emulsify (Fig. 62). The anaerobic type grows 



in the form of discrete colonies, which are only slightly 



adherent to the medium, and are much easier to emulsify. 

 In a glucose agar shake culture the aerobic types give 



a thick pigmented growth confined entirely or almost 



entirely to the surface. The anaerobic type gives a 



characteristic band-like growth situated about 0-5 to 



1 cm. below the surface, with a few larger discrete 



colonies scattered throughout the medium below. No 



growth at all occurs in the upper few millimetres. 

 In broth the aerobic types often form a thick, dry, 



dull, scaly or nodular, pigmented surface pellicle, which 



may extend for some distance up the sides of the tube. 



A ropy or membranous, sometimes pigmented sediment 



forms, augmented by fre- 

 quent deposits from the 

 surface membrane. The 

 broth remains clear, or at 

 most shows a finely granular 

 turbidity. Aerial hyphee 

 may sprout from the surface 

 pellicle. Sometimes growth 

 commences at the bottom, 

 and characteristic fluff-balls, 

 resembling the head of a 

 seeding dandelion, develop. 

 The anaerobic type grows 

 in the form of compact 

 whitish granules with a nod- 

 ular surface deposited at the 

 bottom of the tube ; there 

 is no turbidity and no sur- 

 face growth. Nitrate broth 



is more favourable for 

 Fig. 63. — Actinomyces graminis X 1000. 



Fig. 62.— 

 Actinomyces graminis. 



Culture, 14 days, 37° C. 

 glycerine agar slope, 

 aerobically. 



growth than ordinary broth. 

 The cultural character- 

 istics on other media can 

 be ascertained from the descriptions of the individual species. 



A small granule composed of radiating filaments ; from a 

 broth culture, 24 hours, 37° C. aerobically. 



