CHAPTER XXXV 



BACILLUS TETANI 



(TACK BACILLUS) 



The bacillus tetani is frequently present in dust and soil, especially dust 

 accumulated in old buildings, farms and cattle sheds and in soil enriched with 

 horse and cow manure. 



It is almost constantly present in the intestinal contents and feces of sheep 

 the source of cat-gut used in surgery. 



The comparative frequency with which tetanus has followed black powder 

 burns, would seem to indicate some relation between this substance and bacillus 

 tetani. 



Morphology. It is a straight bacillus 3 to 5 /x long, 0.3 to 0.6 /x wide, has 

 rounded ends, is slightly motile and produces spores. While most spore- 

 bearing bacteria carry their spores in or close to the middle, the spores occur 

 in tetanus bacilli at one end. As they are somewhat larger in diameter than the 

 bacillus itself and cause a bulging, a characteristic tack-like appearance is 

 produced. Tetanus bacilli are arranged singly and in irregular clumps of two, 

 three or four organisms. 



Staining. Bacillus tetani stains with all the usual anilin stains and is 

 Gram positive. 



Growth. Bacillus tetani is primarily an obligate anaerobe; under certain 

 conditions it is also facultative aerobic. Growth occurs at temperatures 

 between i5C. and 44C., best at 37C. 



Bouillon incubated at 37C. under anaerobic conditions becomes cloudy in 

 18 to 36 hours; later a grayish sediment forms and after a week or two the 

 medium becomes clear. An offensive odor, suggestive of burnt horn, is 

 produced. 



Agar. Small, spherical, whitish colonies appear in 36 to 48 hours. They 

 have a dense center surrounded by a thin, irregular zone. 



Stab cultures show a cloudy appearance of the medium, which is split by 

 gas formation. 



Gelatin. Surface growth is similar to that observed on agar. 



Stab cultures in gelatin, as in agar, at first show fine white lines of growth 

 extending at right angles to the stab; as these increase the medium becomes 

 cloudy. Gelatin is slowly liquefied, and when liquefaction is complete a whitish 

 sediment is deposited and the medium becomes clear. 



Blood serum shows nothing characteristic and is not liquefied. 



Potato. The growth of the tetanus bacillus on potato is slight, glistening 

 and colorless. 



Milk is not coagulated. 



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