410 THE HEMORRHAGIC SEPTICEMIA GROUP 



nut oil provided the culture is maintained free from all vibration, 

 causes a characteristic "stalactite" growth; the organisms grow 

 down from the oil droplets as filaments (which have been likened to 

 stalactites) until they even reach the bottom of the tube. Chains of 

 bacilli are most characteristically developed in this medium. The 

 addition of 2 to 3 per cent, common salt to broth or agar stimulates 

 the formation of very irregular involution forms. Milk is not coagu- 

 lated, but a slight permanent acidity gradually develops. Growth on 

 coagulated blood serum or ascitic agar, although somewhat more 

 luxuriant than on ordinary laboratory media, is not characteristic. 



Bacillus pestis is an aerobic organism; it fails to develop with its 

 customary vigor in the absence of oxygen. Unlike a majority of 

 pathogenic bacteria, the optimum temperature of growth is about 30 

 C.; growth ceases below 10 C. and above 40 C. The viability of the 

 organism in cadavers is considerable; they may remain alive for 

 several weeks. In pus and sputum viable cultures may be obtained 

 after one or even two weeks. Exposure to sunlight kills the bacilli 

 within a few hours, and naked germs (unprotected by mucus or 

 other protein envelope) are rapidly killed by drying. An exposure 

 to 58 C. for an hour, or 100 C. for a few minutes is fatal: 5 per cent, 

 carbolic acid and 1 to 1000 bichloride of mercury kill the organisms 

 within fifteen minutes. The virulence of the bacilli diminishes rather 

 rapidly in artificial media as a rule. 



Products of Growth. Indol is not produced in sugar-free broth. 

 Acids, but no gas, are produced in dextrose, lactose, galactose, mannite 

 and maltose, but not in saccharose, sorbite, dulcite, and inulin. 



No enzymes have been demonstrated in cultures of plague bacilli. 



Toxins. Filtered cultures of plague bacilli possess little or no 

 toxicity, although old broth cultures, freed from bacteria by filtration 

 through unglazed porcelain, may exhibit slight toxic action. It is 

 probable that this toxicity is referable to some endotoxin which has 

 been liberated in the medium during the gradual autolysis of the 

 organisms. The symptoms of plague are attributed to the action of 

 endotoxins which are liberated within the host as the organisms dis- 

 integrate. The virulence of plague cultures is variable. Freshly 

 isolated strains may occasionally exhibit almost no virulence for 

 experimental animals, although as a rule they are very virulent. 

 Prolonged cultivation upon artificial media usually results in a decided 

 lowering of virulence, although here again exceptions are met with. 1 



1 McCoy and Chapin, Pub. Health Bull.. January, 1912, No. 53, p. 1. 



