92 



SOLUTIONS AND PROTOPLASM 



[Ch. Ill 



of a capillary tube containing a dense solution, grains of NaCl 

 are placed at one point of the margin of the drop. These 

 grains gradually dissolve, their molecules gradually diffuse 

 through the drop, and as they do so the bacteria retreat before 

 them, remaining in the zone of least concentration. Again, a 

 drop of distilled water was placed alongside of the drop of sea 

 water containing Spirillum, and the two drops were connected 

 by a communicating canal of water (Fig. 11). As the dis- 



Disiilled neater. 



Distilled water. 



Fig. 11. — A drop of sea water connected with a drop of distilled water (in lower part 

 of diagrams) . The marine bacteria of the former retreat before the encroachment 

 of the latter. (From Massaut, '91.) 



tilled water mingles with the sea water at one mouth of 

 the communicating canal, the bacteria retreat further and fur- 

 ther from that mouth, keeping in the most concentrated part 

 of the drop. Finally, when a drop of sea water is connected 

 with one of distilled water, and granules of NaCl are placed 

 in the drop of sea water, the bacteria, retreating from the zone 

 of too great concentration penetrate into the drop of distilled 

 water (Fig. 12), where they now find the proper concentration. 

 Thus, Spirillum is sensitive both to solutions denser and to 

 those weaker than the normal (hyperisotonic solutions and 

 hypisotonic solutions, M assart). 



In summing up the observations of this section, we notice 

 that some organisms (for Massaet found some non-sensitive 

 bacteria) are sensitive to concentration. This sensitiveness is 



