638 MtCROBIAI, DISEASES OF INSECTS 



tents next become liquefied; they are at first a clear yellow, later dark- 

 ening little by little until they are blackish in color. At this stage a 

 slight pressure upon the abdomen causes th^ liquefied intestinal con- 

 tents to issue from the anus and the characteristic diarrhoea reveals itself 

 on the vegetation which is fouled with the dejecta of the sick locusts. 

 Some hours afterward the locust falls upon its side and the legs move 

 spasmodically; the locust remains in this comatose state several min- 

 utes to several hours until death occurs. When the virulence of the 

 coccobacillus is very high', very often the chylific stomach only presents 

 the characteristic blackening; death occurs before the intestinal con- 

 tents have undergone a modification. After death the insect putrefies 

 very rapidly and the tegument becomes dark. 



The intestinal content of locusts attacked with this disease shows 

 microscopically practically a pure culture of this bacillus. The intes- 

 tinal contents of healthy locusts are poor in bacteria, sometimes seem- 

 ingly aseptic. Among the saprophytes found, the most common is a 

 motile. Gram-positive coccobaciUus which ca,uses death of locusts by 

 injection but never by ingestion. It is distinguishable from the specific 

 coccobacillus by the disagreeable odor which it produces in the locusts 

 or in culture media. Sometimes staphylococci are found, rarely B. 

 siibtiUs; only one saprophyte per hundred of the specific bacillus rend- 

 ers the isolation of the latter very simple. 



All of the tissues of the locust are invaded by this bacillus as has 

 been proved microscopically. A pure culture can be obtained from the 

 blood at the same time that the intestinal contents are attacked, thus 

 B. acridiorum produces a veritable septicemia. 



Causal Organism. — E. acridiorum, the causal organism of the Mexican locust 

 epizootic is a short, slightly ovoid baciUus, decidedly polymorphous; in the same 

 culture coccus forms of about 0.6/i are found beside of forms plainly bacilli, o.^ii to 

 o.6jiiXov9/< to i-Sm; actively motile possessing peritrichic flagella; Gram-negative but 

 stains readily with anilin dyes; the baciUus takes the stain most deeply at the poles, 

 especially if Ziehl's carbol-fuchsin is used for one to two seconds. 



Facultative anaerobe; cultures grow readily from 16° to 43° in all ordinary media, 

 even in Raulin's medium. It develops very rapidly at 37° in broth, turbidity appear- 

 ing at about the fourth hour. A delicate membrane is formed on broth which dears 

 only after three weeks, leaving a heavy sediment. Young agar colonies are cir- 

 cular and hjive a waxy appearance; they grow rapidly, being plainly visible after 

 twelve hours; after eighteen hours, they are 2-3 mm. in diameter. Subsurface 

 'colonies are small, spherical, whitish and opaque. Gelatin is not liquefied. 

 Milk is coagulated and rendered strongly alkaline. Grows abundantly on potato 



