3 a THE PSYCHIC LIFE 



significance. If the Micro-organism lives in the 

 water, which is most frequently the case, the oxygen 

 contained in solution therein passes directly through 

 the cellular cuticle by dialysis and comes in contact 

 with the body of the protoplasm; in which case the 

 process of respiration is solely a chemical phenome- 

 non. But it may happen that a minute organism 

 chances into a medium containing little or no oxygen- 

 gas; amid these new conditions where it becomes nec- 

 essary to move towards sources emitting oxygen by 

 voluntary effort and directed motion, it has been dis- 

 covered that a great number of Micro-organisms, and 

 particularly Bacteria, are capable of detecting the ex- 

 pansive power exerted by oxygen in the liquids in 

 which they are found. When bacteria of putrefied 

 matter are put in a drop of water containing no oxy- 

 gen but in which have been placed chlorophyl algae, 

 or green Euglenae, or grains of chlorophyl obtained by 

 crushing green cellules, nothing happens in the first 

 instant; but if the preparation be illuminated so as to 

 allow the chlorophyl to act, the bacteria are seen to 

 exhibit very rapid movements and to proceed, al- 

 together, towards the points of the preparation where 

 the generation of oxygen is taking place, that is to 

 say, about the grains of chlorophyl. Under these con- 

 ditions a chemical exchange is instituted between the 

 chlorophyl and the aerobious Bacteria: the Bacteria 

 disengage carbonic acid gas and absorb oxygen; the 

 chlorophyl fastens upon the carbon of the acid and 

 sets the oxygen at liberty. If the preparation be 

 darkened the Bacteria cease assembling about the 

 chlorophyl grains, which, hid from the light, cease to 

 disengage oxygen. The clustering begins anew, if a 

 ray of sunlight is again let touch the chlorophyl. 



