56 ACTIVITIES OF BACTERIA. 



tile hog-cholera bacterium ; and motile pest cultures and 

 motile bacteria of septicaemia hsemorrhagica have been de- 

 scribed in isolated instances. Compare also what is said 

 in the special part regarding the Bac. implexus. 



As first shown by Pfeffer, many chemical substances ac- 

 tively attract (positive chemotaxis) and others repel bac- 

 teria (negative chemotaxis). Oxygen is particularly at- 

 tractive for aerobic and repellent for anaerobic bacteria. 

 Like Beijerinck, one may obtain very beautiful chemotaxic 

 or aerotaxic figures in the following manner : An un- 

 sterilized pea or bean is placed in a test-tube which is three- 

 quarters full of sterile water. The bean gives off nutrient 

 materials by diffusion, which slowly extend upward. In 

 this weak nutrient material certain varieties of bacteria in- 

 troduced with the bean develop at sharply defined hori- 

 zontal levels, which slowly extend toward the top. Cer- 

 tain varieties form several layers above one another. I 

 have had these interesting statements verified by Mr. 

 Miodowski, and have substantially confirmed them, with 

 the exception that we found a bacterium related to the Bac. 

 mesentericus and the Bac. subtilis predominantly present, 

 instead of the non-sporulating Bac. perlibratus Beij., which 

 Beijerinck found to principally compose the layers. (Com- 

 pare Beijerinck, C. B. xiv, 827; C. B. L. in, 1; and 

 Miodowski. Dissert. Wiirzburg, 1896.) In his second 

 work especially, Beijerinck has related a number of inter- 

 esting observations, but I am unable to enter into details 

 regarding them, nor upon the analogous studies of Jegu- 

 now (C. B. L. n). 



Schenk has observed a positive thermotropism. If a 

 hanging drop is warmed at one point by a warm wire 

 (temperature difference of 8 to 10), the bacteria strug- 

 gle toward it (C. B. xiv, 33). 



2. OPTICAL ACTIVITY. 



There are found, fairly widely distributed, especially 

 in media rich in salt (sea- water, Elbe, salt-fish), fission 

 fungi which emit light, of which a considerable number, 

 mostly bacteria and vibriones, have been studied. The 

 phosphorescence is a life=symptom of the bacteria and 



