54 



THE CELL 



around the alga drawn by the oxygen which is set free by the chlorophyll (Fig. 

 31, Engelmann). 



If a capillary tube, fused at one end, be filled with a 0.05-per-cent solution 

 of malic acid and the open end of it be placed in a drop of water containing 

 the spermatozoids of a fern, so that the acid can diffuse gradually into the water, 



FIG. 31. Illustrating chemotaxis. The chlorophyll bodies in the cells of Mesocarpus scalaris 

 under the influence of light liberate oxygen : the bacteria are most abundant where the chlo- 

 rophyll bodies lie nearest the surface i. e., where the liberation of oxygen is most active, 

 after Engelmann. 



the spermatozoids begin at once to move toward the opening of the tube and to 

 wander into it. The same phenomenon may be observed indeed with a much 

 weaker solution (0.001 per cent, Pfeffer). 



It has been observed that the uterus and Fallopian tubes of rabbits and rats 

 exercise a positive chemotactic influence on the spermatozoa of the correspond- 

 ing species, but that the ovary itself is entirely indifferent in this respect. Chemo- 

 taxis is of the utmost importance in the following connection also. We have seen 

 how the leucocytes have the power to seize and consume Bacteria which find 

 their way into the body. They are attracted to the Bacteria by substances given 

 off by those organisms. If a capillary tube, containing a sterilized culture of, 

 say Staphylococcus pyogenes albus, be introduced under the skin of a rabbit, 

 after a few hours it is filled with leucocytes. The same culture fluid by itself 

 exercises 110 such influence on the leucocytes. 



Likewise when the leucocytes assemble in a certain place for the purpose 

 of carrying away the products of normal or pathological tissue destruction, their 

 migration is caused by chemotaxis (cf. page 37). In short, as far as our present 

 information goes, we may say that the migrations of the leucocytes are con- 

 trolled, quite independently of the nervous system, essentially by chemotaxis. 



From these examples it ought to be apparent that chemotaxis plays a very 

 great role in the processes of the living world, since by it the migrations of 

 free-living cells are often controlled according to their momentary needs. It 

 is therefore unnecessary to invoke any psychical properties in explanation of 

 such phenomena. 



In the higher animals the sense of smell has been developed as a special 

 chemical sense. It is true that many of the movements taking place under 

 its influence are to be regarded as conscious; but in many other cases they 

 run the course of pure reflexes., and if we may extend the notion of chemo- 

 taxis to all movements which either directly or indirectly are inaugurated 

 and controlled by chemical stimuli without the participation of consciousness, 



