346 Illinois State Lahoratoj^ of Natural History. 



affected by the amount of moisture, by the temperature, 

 and by all conditions affecting the vitality of the organ- 

 ism. These radiations are apparently more abundant 

 where the amount of moisture is considerable and the 

 temperature about the optimum, but with too much 

 moisture the bacillus spreads over the surface as a con- 

 tinuous sheet-like growth. Where the colonies are very 

 abundant they remain small and circular, or become 

 variously united in a complete network. At low tem- 

 peratures the lobulations seldom occur. I have also 

 made Petri-dish cultures from tubes kept for some time 

 in the laboratory, and on agar containing varied quan- 

 tities of water, but these marked growth characters were 

 then entirely absent. This may be due to a lessened 

 motility of the bacillus, or to other causes not wholly 

 understood. 



After being grown in the laboratory in several suc- 

 cessive tube cultures, this organism seems to lose the 

 power of producing the slight yellowish-white color, and 

 the growth becomes a purer opal white. 



It should be noted that in subsequent isolation cul- 

 tures, it was found that the pathogenic form could 

 often be secured pure, even in the first dish, by using 

 sick insects, observing proper sterilization precautions 

 in clipping off a leg in the region of the femur, and 

 transferring to the tube with a platinum needle a little 

 of the exuded fluid. The fluids of the diseased bug are 

 almost pure cultures of the pathogenic organism, and 

 unless the alimentary tract is badly broken down, I have 

 seldom found man^^ foreign germs. 



From the above notes it will be seen that with this 

 bacillus there is apparently no tendency towards spon- 

 taneous variation in the colonies growing side by side 

 in a culture direct from the insect. I have also care- 

 fully observed the growth in cultures from various 

 sources, and the more marked opalescence after contin- 

 ued growth on agar is the only variation noted. 



