THE EFFECTS OF BACTERIA. 113 



bean gives off nutritive substances, which slowly ex- 

 tend upward. In this feeble nutrient solution cer- 

 tain bacteria which have been introduced with the 

 bean develop in sharply defined horizontal planes, 

 which slowly ascend. Certain varieties form several 

 planes above one another. I have had these interest- 

 ing statements investigated by Mr. Miodowski, who 

 corroborated them in great measure. But instead of 

 the non-sporulating bacillus perlibratus Bey., which 

 usually formed the planes in Beyerinck's experi- 

 ments, we found chiefly an organism allied to ba- 

 cillus mesentericus and bacillus subtilis (vide Bey- 

 erinck: C. B., XIV., 827, and Miodowski: Diss., 

 Wiirzburg, 1896). 



Schenk has observed a positive thermotropism. 

 If a hanging drop containing bacteria is warmed at 

 one point with a warm wire (temperature difference 

 8-10) the bacteria congregate in that spot (C. 

 B., XIV.). 



2. OPTICAL EFFECTS. 



Phosphorescent bacteria are distributed quite 

 widely, especially in and near salty media (the ocean, 

 rivers, salted fish) , and a considerable number main- 

 ly bacilli and vibriones have been carefully studied. 

 Phosphorescence is a vital symptom and does not 

 depend upon the oxidation of a photogenic substance 

 secreted by the bacteria (K. B. Lehmann and Toll- 

 hausen : C. B. , V. , 785) . It is destroyed by all factors 

 which injure the life of the bacteria; cold produces 

 rigidity of the organisms and interrupts the phos- 

 phorescence as long as it lasts. High temperatures, 

 acids, chloroform, etc., interfere temporarily with the 

 8 



