852 BACILLUS 



Pigment. — None. 



Antigenic Structure. — Spore antigen is difFtTent from that of B. mhtilis or B. vulgatus. 



B. megatherium de Bary. 



First described by de Bary in 1884, who found it on cooked cabbage leaves. 

 It is one of the largest members of the Bacillus group, and occurs in dust, soil, air, 

 milk, and water. Morphological and colonial variants have been described by 

 Knaysi (1933). According to Rettger and Gillespie (1935), the well-known morpho- 

 logical pleomorphism of this organism is governed largely by environmental con- 

 ditions, particularly oxygen starvation. It forms a powerful ha^molysin (Todd 1901, 

 1902, Warden et al. 1921), most active towards the red corpuscles of man, monkey, 

 and the guinea-pig ; it appears in broth cultures at 37° C. on the 2nd or 3rd day, 

 increases to a maximum on the 6th or 7th day, and then diminishes slowly. Oxygen 

 is essential for its production. The haemolysin, which can be filtered through a 

 Pasteur-Chamberland candle, deteriorates rapidly on keeping, and like many other 

 true toxins is destroyed by heating at 56° C. for half an hour. Subcutaneous injec- 

 tion into guinea-pigs gives rise to a large local swelling with subsequent necrosis. On 

 intravenous injection into guinea-pigs it gives rise to hsemoglobinuria, but is not 

 fatal except in large doses — about 10 ml. Antihaemolysin can be prepared by 

 injection of the haemolysin into goats. Warden, Connell and Holly (1921) found 

 that when 2 ml. of centrifuged broth culture were injected intraperitoneally into 

 guinea-pigs, the animals died in less than 12 hours. Post mortem the abdomen 

 was distended, the peritoneum congested, there was hsemolysed blood in the 

 peritoneal cavity, and bloody fluid in the lumen of the gut, in the pleural cavities 

 and over the thighs. They bring evidence to suggest that the toxin and the 

 haemolysin are one and the same body. 



Bacillus megatherium de Bary 

 SynoJiyms. — Probably represents some strains known as B. anthracoides or B. pseudo- 



anthracis. 

 Habitat. — Found in dust, soil, water, milk. 



Morphology. — Large, rod-shaped, 3-9 ^ X 1-2 fi. Long 

 ^0^ unsegmented forms are common, and shadow 



^^^^^HHil^^ forms appear early. Ends shghtly rounded, axis 



^m Jj^^^^^^K^kt. curved ; occurs singly, in pairs and in chains. 



^V ^^^^^^^^^Hk Cells contain fat globules. Motile by 4-S peri- 



ls ^^^^^^^^^IB trichate flageUa. Spores equatorial, oval, or 



^B ^^^^^^^^^^^He ellipsoidal, not bulging ; germination by absorption 



^K '^^^^^I^^^^HF of spore coat. Non-capsulated. Gram-positive. 



^^K ^I^^^^^^Bf Non-acid-fast. 



^fc ^^^^^^^ Agar Plate. — Round, 3-5 mm. in diameter, raised, dull, 



^*y greyish-white, opaque colonies with entire edge 



and finely granular surface, sometimes radially 



Fig. 188. — B. megatherium. striated ; may show differentiation into raised 



Surface colony on agar, 36 opaque centre and thin translucent periphery ; 



hours, 37" C. ( X 8). membranous consistency ; emulsiiiabihty fairly 



easy. After about a week irregular round scales 

 appear on the surface of the colony, similar to those on anthrax colonies. 

 Agar Slope. — Profuse, moist, raised, glistening, greyish-yellow, creamy growth with smooth 

 surface and entire edge ; butjTous consistency ; sometimes may show parallel 

 raised ridges like contour lines ; emulsifies easily. After about a week irregular 

 round scales appear on the surface of the growth, similar to those of anthrax. 



