318 SPECIFIC MICRO-ORGANISMS 



stained the ends become deeply colored while the equator remains 

 pale (bipolar staining) . Alongside this typical form many irregu- 

 lar organisms are usually found, especially longer and shorter 

 bacilli, some pale, some irregularly outlined, and some swollen 

 and poorly stained. The last-mentioned types of bacilli are more 

 frequently found in the bodies of plague victims which have be- 

 gun to decompose. They are also observed in artificial cultures. 

 These irregular forms (involution forms) are important in the 

 quick recognition of plague. The bacillus stains very readily, 

 best with methylene blue or with a momentary exposure to carbol- 

 fuchsin. Better results are obtained by fixing the spread in alco- 

 hol one minute, rather than heating it. The Romanowsky stain 

 gives good results. It is distinctly Gram-negative (contrary to 

 the original statement of Kitasato). Capsules may be demon- 

 strated on bacilli in the peritoneal exudate of guinea-pigs and 

 mice, less easily in cultures. It is non-motile and flagella have 

 not been demonstrated. Spores have not been observed and 

 cultures are killed at 60 C. in 10 to 40 minutes. It is also easily 

 destroyed by chemical germicides, for example, by 5 per cent car- 

 bolic acid in i minute. Mere drying at 35 to 37 C. kills the 

 bacillus in two to three days, but at 20 C. it may withstand drying 

 for 20 days. It may live for months in frozen material. 



Cultures are readily obtained on ordinary media, best at a 

 temperature between 25 and 30 C. Growth is moderately 

 slow. Gelatin is not liquefied. On agar containing 3 per cent 

 of sodium chloride, irregular involution forms areprodu ced in 24 

 to 48 hours. Long chains are produced in broth. It does not 

 form gas from sugars but does produce acid from dextrose, levu- 

 lose, mannite and galactose, not from lactose or dulcite. 



The toxins of the plague bacillus are in part soluble and in 

 part intimately combined with the bacterial cell. Filtrates of 

 young broth cultures are without toxic properties but older broth 

 cultures (14 days) yield a toxic filtrate. The bacterial cells killed 

 by heat produce fatal poisoning in guinea-pigs and rabbits. 

 The poisons obtained so far are much less powerful than the sol- 



