CHEMOTAXIS 41 



useful treatise on this question, examined more closely the methods of topo- 

 graphical arrangement adopted in liquid media by various motile bacteria under 

 the influence of oxygen, which arrangement he called respiration figures. Some 

 of these are shown in Fig. n. 



From the researches of Stahl and De Bary, and especially those of W. 

 PFEFFER (I.), we learn that not only oxygen, but also various other substances,, 



FIG. ii. Respiratiou figures of motile bacteria. (After Beyerinck.) Natural size. 



The three figures are horizontal projections of bacterial preparations, each in a large drop of water. 

 The three large circular cover-glasses only are shown, the slides not being reproduced. A small 

 platinum wire (not shown in the figures) is placed at the part represented by the top of the drawing, 

 between the cover-glass and slide, so as to form a wedge-shaped space, which is occupied by the drop of 

 water, the base of which lies in m ( = meniscus). 



The three figures represent : 



I. Respiration figure of the aerobic type. The roving individuals collect in the oxygenated 

 border zone (), whilst the quiescent ones (r) remain in the interior, leaving a vacant space {/) between 

 the two. 



II. Respiration figure of the spirillum type. These organisms require and tolerate only 

 traces of oxygen. They therefore collect, not at the circumference of the drop, but at a little distance 

 therefrom (sp), where the tension of the penetrating gas is lower. 



.III. Respiration figure of the anaerobic (air-shunning) type. These migrate to the centre 

 (an) of the drop, as being the place of lowest oxygen content. 



are capable of attracting or repelling bacteria and other micro-organisms, a 

 faculty to which the name of positive or negative chemotaxis has been given. 

 Use is made of this property in order to capture the motile species in a 

 bacterial mixture by introducing therein a capillary tube filled with a solution 

 of a substance which exerts an attractive influence on one or other of the motile 

 species. 



Among the inorganic compounds the salts of potassium have the greatest 

 power of attraction, and are therefore most frequently employed for this 

 purpose. Of the organic compounds, asparagin is particularly effective. The 

 sap or juice of raw potatoes contains both these lures, and is therefore highly 

 efficacious. More particular information on this method of isolation is given by 

 ALI-COHEN (II.). 



The attractive power of such agents is not limited to motile bacteria alone, 

 but also extends to higher sessile fungi. If such an attracting agent be 

 brought sufficiently near to a culture of the latter description, the growth and 

 extension of the cell threads on that side of the culture will show marked 

 exuberance. This attempt on the part of sessile fungi to turn towards a point 

 of chemical attraction is entitled Chemotropism. Its cause is identical with 

 that of Chemotaxis ; the difference in the effect being due to the difference of 

 the object influenced. It may be mentioned that MIYOSHI (I.) has performed 

 exhaustive experiments of this kind. 



