1923] 



JENNISON — POTATO BLACKLEG 17 



not extended, the writer was led to assume that a single organ- 

 ism caused the potato blackleg disease in North America. 



A study of the literature was begun, and it was soon learned 

 that at least 4 different species of Bacillus had been described 

 by as many authors as the cause of the disease under considera- 

 tion. 



By comparing the following descriptions it will be seen that 

 the "species" in question do not differ markedly. In the sum- 

 maries presented no attempt is made to follow the original form, 

 but accuracy of statement is preserved. 



Bacillus atrosepticus van Hall. — The following was prepared 

 from a translation 1 of van Hall's ('02) original description. It 

 bears comparison with that prepared for Morse ('17) by Dr. R. 

 de Zeeuw. 



Morphology : B. atrosepticus is a rod-shaped bacillus, occurring for 

 the most part singly, rarely in pairs, in 2-day-old bouillon cultures at 

 27 °C. Size variable; length 0.8-1.6 (j, breadth 0.2— .4 p. Many zoogloea 

 of 4-10 organisms. The bacteria are very active in a 24-hour culture 

 of distilled water plus 0.025 per cent potassium phosphate and 0.25 

 per cent asparagine (27 °C). Material stained by Loeffler's method. 

 Length of flagella 10-15 u. Gram negative. 



Cultural characteristics : Gelatin liquefied, rapidity variable. 

 Growth on malt gelatin and malt agar very weak. Milk coagulated. 

 Growth best at top of meat agar stab. 



Physiology: Growth very strong at 27 °C. Thermal^ death point 

 51-52 °C. Facultative anaerobe. Reduction of methylene blue weak. 

 Nitrates reduced to nitrites. Sodium selenite reduced rapidly. No 

 diastatic action. No indol production. No H 2 S produced in broth 

 cultures. The organism is a weak gas producer (except when man- 



nite is present). Gas produced from glucose, saccharose, and mannite 

 in a medium made by adding to "due water" (a filtered w r ater) 0.025 

 per cent K 2 HPO.i, 1 per cent peptone and 3 per cent of sugar. No gas 

 from lactose and glycerin in same medium. Growth slow at first in 



bouillon acidified to a reaction of 0.5 per cent normal with citric and 

 malic acid. Organism grows poorly when transferred from dried cul- 

 tures: thought not to be resistant to drying. Pathogenic to potato 

 stems and tubers. Index No. 5312-32120-2121. 2 



Bacillus phytophthorus Appel. — The following is summarized 

 from Appel's ('03) diagnosis: 



2 My thanks are due to Dr. J. C. Th. Uphof for assistance rendered in translat- 

 ing Part III of van Hall's ('02) dissertation. 



2 "Index Number" digits throughout this paper are arranged according to the 

 Descriptive Chart indorsed by the Society of American Bacteriologists, Dec. 30, 

 1920. 



