294 INFECTION AND RESISTANCE 



idea was suggested by Quincke, 45 and later by Biitschli, 46 but has 

 been most extensively studied by Rhumbler. 47 The result has been 

 the production of a number of "artificial amebse" which in almost 

 all respects behave like the living organisms. Thus if a small mass 

 of mercury is placed into a dish filled with water acidified with 

 nitric acid, and a small crystal of dichromate of potassium is dropped 

 near the mercury, the dichromate will dissolve and a yellow cloud 

 will gradually diffuse from it toward the mercury. As soon as the 

 yellow cloud touches this it will begin to show change of form and 

 to elongate in the direction of the dichromate, often moving to- 

 ward it. The motion of the quicksilver will resemble with con- 

 siderable accuracy that of an ameba moving toward a particle of 

 food or sending out pseudopodia. A more striking and complete 

 imitation is that obtained by Rhumbler when he placed a drop of 

 clove oil into a mixture of alcohol and glycerin. The changes of sur- 

 face tension produced upon the surface of the clove oil by the alcohol 

 give rise to movements in the oil entirely analogous to those of mo- 

 tile cells in favorable media. The similarity has been extended 

 even to the processes of engulfment of the food as observed among 

 amebse. Thus a drop of chloroform in water will flow about a 

 particle of shellac and dissolve it. If a piece of glass coated with 

 shellac is placed in contact with the drop it will engulf it, 

 but will cast out the glass after the shellac coating has been dissolved 

 away. 



The similarity between phenomena purely referable to surface 

 tension and those taking place in the living cells is therefore very 

 striking and has been clearly analyzed in regard to its bearing 

 upon leukocytic chemotaxis by Gideon Wells in his "Chemical Path- 

 ology." The chemotactic substances, diffusing to the leukocyte, will 

 lower its surface tension on the side at which they come in contact. 

 Pseudopodia will be thrown out on this side in consequence, and the 

 leukocyte will move in this direction. The motion will be continued 

 in this direction as long as the concentration of the chemotactic sub- 

 stance, and therefore the diminution of surface tension is greater on 

 this side than on other parts of the periphery, until a point is reached 

 at which the chemotactic substance is equally diffused on all sides, and 

 motion will cease. The actual engulfment may then occur or the 

 nature and concentration of the chemotactic substance may be so 

 great that injury is done to the leukocyte. Whether or not the purely 

 physical explanation of chemotaxis tells the whole story it is of course 

 not possible to decide. At any rate, it furnishes a rational basis for 



45 Quincke. Quoted from H. G. Wells, "Chemical Pathology/' Saunders, 

 1907. 



46 Biitschli. "Untersuch. iiber mikroskopische Schaume und das Proto- 

 plasma." Leipzig, 1892. See also H. G. Wells, loc. cit., pp. 220 et seq. 



47 Rhnmbler. Arch. f. Entwickelungs Mechanik, 1898. 



