14 



BULLETIN SO:), U. S. DEPARTMENT OF AGRICULTURE. 



Motility. — The bacillus is moderately motile in young cultures taken from the 

 surface of brood-filtrate agar but is somewhat more sluggish when grown in liquid 

 cultures. 



Spore formation. — On brood-filtrate agar evidence of spore formation is present 

 about the third day. The rod is swollen near the center where the spore is formed, 

 being then spindle-shaped (fig. 3; PI. VII, B). In a few days numerous spores free 



Fig. 1.— Bacillus larvae: Vegetative form. 



from the rods are to be seen (fig. 4; PI. VII, D). They measure about 0.6 by 1.3 ju- 

 In some environments few or no spores are produced. This occurs in liquid media, 

 deep in solid media, and on media containing glycerin, mannite, or glucose. Some 

 of the other sugars and also honey inhibit spore formation. 



Staining properties. — The rods color readily and uniformly with the analine stains, 

 and are Gram-positive. The spores are quite resistant to stains. 



Fig. 3. — Bacillus larvae: Spore formation. 



Fig. 4.— Bacillus larvae: The spores. 



Oxygen requirements. — ^Yhen bee larvae agar alone is employed and inoculations 

 are made with spores following Liborius' method for anaerobes, growth as a rule has 

 appeared more often near to than on the surface (PL VIII, E, F, G, H, I). Subcul- 

 tures on brood-filtrate agar (PI. VIII, D) and egg-yolk-suspensicn agar or their 

 combination yield abundant surface growth. 



Agar slant. — On the surface of inclined brood-filtrate agar subcultures (PI. VIII, D) 

 grow rapidly, producing a moderate to heavy growth in 24 hours. This growth tends 



