Waksman — 34 — Actinomycetes 



ter. They are soft and easily broken under light pressure, but they 

 may occasionally be tough or even calcified. The crushed granule ap- 

 pears as a disorganized mass of irregular, bent and branching filaments, 

 some of which may terminate in the characteristic clubs. In prepara- 

 tions fixed and stained by Gram's method the structure of the granule 

 is lost, the clubs not showing and the picture being that of a mass of 

 irregular bent gram-positive rods. 



The morpholog)' of the organism has been described as varving from 

 a compact mass of branching mycelium of gram-positive filaments to a 

 mass of short rods which mav be evenly stained or granular, and which 

 show no indication of branching. These differences were found to be 

 associated with roughness or smoothness of the colony. Rough colo- 

 nies, whether grown on an agar surface or in an agar shake culture or 

 in broth, show regular branching; twig-like forms are, however, much 

 more common than long filaments. Intermediate and smooth colonies 

 give a picture resembling that of the diphtheria organism, with granular 

 and polar-stained forms, and with suggestive evidence of branching. 

 Some of the smooth colonies may be derived from rough and clearly 

 branched forms by subculturing; they show evenly stained rods with no 

 distinguishing characteristics. The rough and intermediate forms often 

 show terminal swellings or "clubbed forms" similar to those of the diph- 

 theria organism; but the true clubs do not appear in cultures. 



White or grayish colonies up to about 1.5 mm. in diameter, are pro- 

 duced in glucose-agar shake cultures at 37°C. within 3 to 6 davs. The 

 rough strains grow in a zone about 5 mm. wide, the upper limit being 

 0.5 to 2 cm. below the surface of the agar. A few colonies may be pres- 

 ent below or above this zone, but no growth takes place on the surface. 

 Smooth strains show no zone of concentrated growth; the colonies are 

 uniformly distributed from the bottom of the tube to a level 0.5 to 1 cm. 

 from the surface, where growth terminates abruptly. When a colony 

 of a rough strain is transferred with a capillary pipette to a slide, it is 

 usually found to be tough and difficult to break up and emulsify; it 

 shows the characteristic compact branched mycelium. 



Rough strains grow in glucose broth at 37 °C. as white or grayish 

 masses up to about 5 mm. in diameter at the bottom of the tube, the 

 medium itself remaining perfectly clear. They are often difficult to 

 break up. Intermediate strains tend to grow as smaller particles or gran- 

 ules either at the bottom or along the side of the tube, or as viscid or 

 flocculent masses, with little or no general turbidity. Smooth strains, 

 however, may produce uniform turbidity with or without a viscid or 

 granular sediment. 



On glucose agar or on brain-heart agar, incubated anaerobically with 

 5 per cent COo for 4 to 6 days, rough or intermediate strains of A. hovis 

 produce white-gravish to yellowish colonies having a diameter of not 

 more than 1 to 3 mm. These colonies usually adhere to the medium, 

 so that they are hard to remove with an iiwculating needle, often com- 



