PHAGOCYTOSIS 287 



and it has been found that in addition to malic acid compounds many 

 other substances, organic and inorganic, occurring in plant cells and 

 cell-sap exert positive chemotactic power. Lidforss has shown, for 

 instance, that calcium chlorid in 0.1 per cent, solution may strongly 

 attract plant spermatozoids (equisetum horsetail). When the solu- 

 tion is concentrated to 1 per cent., attraction is still exerted, but the 

 spermatozoids immediately lose their motility upon entrance into the 

 fluid. 



The same worker has shown that a substance which is positively 

 chemotactic for one variety of plant cell may be negatively chemo- 

 tactic for another, showing a certain selective variation which should 

 be of great biological importance. Thus capillaries with a 1 per cent, 

 solution of potassium malate actively attracted the spermatozoids of 

 marchantia (a liverwort), while not a single spermatozoid of equi- 

 setum would enter these tubes. Low 29 has applied these methods of 

 study to the investigation of the chemotaxis of mammalian sperma- 

 tozoa and found that these cells were actively attracted by weakly 

 alkaline solutions. 



Studies upon the factors determining the movement of bacteria 

 and ameba3 toward some substances and away from others have been 

 numerous, and are valuable for the understanding of leukocytic 

 chemotaxis, because they have led to the formulation of a number of 

 important general theories. The fact that the motions of bacteria 

 in suspensions are, to a certain extent, determined by the negative 

 electrical charge which they all carry in neutral media, has been 

 touched upon in the section on agglutination. Attempts on the part 

 of Young and the writer to determine whether the attraction of 

 leukocytes toward bacteria might be due to the carrying of an elec- 

 tropositive charge by the white cells have met with no result, owing 

 so far to the failure to elaborate a reliable technique. However, this 

 thought is not an impossible one and should be borne in mind. 



That certain bacteria will wander actively toward a source of 

 oxygen was shown by Engelmann' s 30 classical experiment in which a 

 diatom, half in the shade and half in the light, was surrounded by an 

 emulsion of bacteria, and these were seen to collect about the lighted 

 half only, where oxygen was being liberated by virtue of the chloro- 

 phyll. The extreme delicacy of chemotactic reactions is illustrated 

 in these experiments in that Engelmann calculated that the bacteria 

 reacted to one one-hundred billionth of a milligram of oxygen. The 

 selective reaction of bacteria to various chemical substances, further- 

 more, has been shown by allowing different solutions to diffuse into 

 bacterial emulsions from capillary tubes, and by observing attraction 

 or repulsion from the point of contact. 



The chemotaxis of leukocytes has opposed more difficulties to 



29 Low. Sitzungs Berichte kais. Akad. d. Wiss., Wien, Vol. 3, Abf. 3. 



30 Engelmann. Arch. f. d. ges. Physiol, Vol. 57, p. 375. 



