536 THE PATHOGENIC BACTERIA. 



Another disease of potato-tubers quite distinct from the 

 above is " wet-rot," which is widely distributed, and has been 

 known since 1845. It appears on the field and shows itself 

 by a putrefaction of the tubers. Kramer investigated tubers 

 whose contents bad liquefied inside the swollen skin. They 

 contained unaltered starch-grains, remains of the protoplasm, 

 and numerous bacteria. The mass in the earlier stages was 

 acid, later it became alkaline, and smelt strongly of butyric 

 acid. Kramer obtained pure cultures of the bacteria and infected 

 potato tubers in various ways, obtaining in every case the 

 characteristic rot. The Bacillus was obtained in the form of 

 rods with rounded ends, or as long wavy filaments, or as 

 spores. On nutritive agar-agar, the colonies form little dirty- 

 white slimy drops with a distinct margin and a brownish 

 centre. On gelatine the margin of each colony makes a groove 

 or funnel in which the colony lies, and liquefaction of the 

 gelatine proceeds rapidly. This Bacillus is aerobic, in this 

 respect differing from Clostridium butyricum Prazm, which is 

 anaerobic. It also differs from Bacillus butyricus Hueppe, in 

 that it is able to decompose milk. It appears quickly on 

 wounds of all kinds, and infection can easily be performed 

 artificially by pricking or otherwise wounding the periderm. 

 Infection also takes place through uninjured skin, and in 

 this case the Bacillus must enter by the lenticels of the 

 tuber. 



The disease begins with the formation of a soft spot under 

 the periderm of the tuber. This extends rapidly, the tissue 

 being completely destroyed, and leaving great cavities containing 

 the almost uninjured starch-grains. At this stage carbonic 

 acid and butyric acid are formed, so that the reaction to lit- 

 mus is acid ; later the decomposing fluid becomes alkaline 

 from formation of ammonia, methylamine, and trimethylamine. 

 Various putrefactive bacteria and fungi make their appearance 

 in the later stages of decomposition after the periderm has 

 been ruptured. 



A somewhat similar disease is reported by Halsted l from 

 the Southern States of America. Diseases of a similar nature 

 are also reported on tomato, cucumber, and melon. 



1 Zi-ilxi-h rift f. Pfdirj iiL-rioikhi iti-n, 1S95, p. 337. 



