AMERICAN FOULBROOD. 



15 



to spread somewhat from the area inoculated, is grayish- white, and slightly viscid. 

 It presents a more or less uniform border, a smooth surface, and a ground-glass appear- 

 ance. Older cultures are less prominent than the younger ones. 



Agar plates. — Colonies on the surface of agar vary in size depending upon the num- 

 ber present. When only a few are present not infrequently they spread and attain 

 a diameter of a centimeter or more. The border is clearly defined and uniform. 

 The growth is only slightly raised and has a smooth surface and a ground-glass appear- 

 ance (PI. VIII, A, B). Deep colonies vary from lenticular to irregular in form 

 with filamentous outgrowths from portions of their surface (PI. VIII, A, C). 



Fermentation. — Carbohydrate liquid media as ordinarily prepared are not suitable 

 for the growth of Bacillus larvae. In some of these after a considerable period a slight 

 growth may appear at the bottom of the tubes. A little brood-filtrate or egg-suspension 



Fig. 5. — Bacillus larvae, illustrating an inter- 

 esting feature of the organism. 



Fig. 6. — Giant whips from cultures of Bacillus 

 larvae. 



added to the media improves it. No visible gas is formed but in some instances slight 

 acidity is produced. 



Gelatin. — No growth takes place in plain or in brood-filtrate gelatin at tempera- 

 tures at which it remains congealed. 



Power to resist disinfectants. — The spores of Bacillus larvae are very resistant to 

 heat. When suspended in water the more resistant ones require as much as 100° C. 

 maintained for 11 minutes to destroy them and when suspended in honey require 

 a half hour or more (p. 22). They resist respectively 5 per cent carbolic acid for 

 months; 1 to 1,000 mercuric chlorid for days; 10 per cent formalin for hours; and 20 

 per cent formalin for minutes; each acting at room temperature. 



Pathogenesis. — Bacillus larvae is pathogenic for the brood of honeybees. Infection 

 takes place during the feeding period of the larvae by way of the alimentary tract. 

 The brood dies of the disease in the larval, prepupal or early pupal stages. The 

 earliest symptoms to be observed following inoculation usually occur in prepupae 

 during the seventh day after the feeding, rarely earlier. The earliest evidence of 

 infection in pupae occurs one or two days later. The bacilli are at this time distributed 

 throughout the body. Adult bees, rabbits, guinea pigs, and rats are not susceptible 

 to infection with the parasite. 



While the dead brood in the scale stage and in other later stages 

 of decay in American f oulbrood invariably contains spores of Bacillus 

 larvae in immense numbers, a microscopic examination of earlier 

 stages shows not only few spores but also a comparatively small 



