MOVEMENTS OF IRRITATION. 



429 



dish. Emulsion figures 

 are to be referred to cur- 

 rents in the fluid, de- 

 pendent themselves on 

 temperature relations. 

 The emulsion figures have 

 a very great similarity 

 to the figures in which 

 zoospores arrange them- 

 selves under the condi- 

 tions described above, and 

 the same causal forces 

 underlie all these phe- 

 nomena. 



It is also of consider- 

 able interest to study the 

 influence of various sub- 

 stances on the movement 

 of bacteria swarmers. 

 The aerotactic behaviour 

 of these swarmers has 

 already been indicated in 

 11. We will now in- 

 vestigate their so-called 

 chemotactic movements.* 4 



We kill a pea see 

 by immersion in boiling 

 water, put it into 100 c.c. 

 of water, and let it stand 

 for a day or two, till 

 large numbers of Bac- 

 terium termo have developed in the fluid. The fluid is filtered 

 through coarse paper, to remove the larger aggregations of 

 bacteria, and at once employed for the observations. 



Under higher powers we see that .the swarmers of Bacterium 

 termo move slowly or rapidly, sometimes forwards, sometimes 

 backwards. We now apply to the bacterium-containing drop, 

 lying on the bare slide, a capillary tube containing the solution 



FIG. 139. Emulsion figures. (After Sachs.) 



* Of course the movement of the organisms to places relatively rich in 

 Oxygen is itself only a particular example of chemotaxis. 



