ELECTROKINETICS 383 



healing secretions, or hormones. Our present question is, What 

 lets the white blood cell "know" that it is needed at a certain 

 locality? One possible interpretation is given by Abramson. 



Differences in potential arise in tissues incidental to injury. 

 The surface of a wound is negative on the outside and positive 

 on the inside, as in the case of the apple (Fig. 154). Leucocytes 

 are negative and may therefore be electrically attracted to the 

 positively charged injured region. The deduction drawn is that 

 the migration of leucocytes to an injured region is dependent upon 

 electromotive forces present in the tissues. Any cell would tend 

 to move toward the positively charged wounded area, but only 

 the leucocytes can pass through the intervening tissue, for they 

 possess the power of amoeboid movement. Their electric charge 

 and that of the injured tissue merely indicate the direction of 

 migration. (A fact worthy of note is that leucocytes behave like 

 proteins in their cataphoretic properties, while red cells do not.) 



Such theories are highly speculative but rest on experimental 

 results. Obviously, they are not conclusive. Other factors 

 may play a part, J. Comandon has illustrated, by moving 

 pictures, that leucocytes will move toward a starch grain from 

 quite a distance with extraordinary rapidity and in a remarkably 

 straight path, pushing the red blood cells aside as they go. 

 (Starch is insoluble in water ; in the blood, it is broken down into 

 sugars by enzymes ; the sugars go into solution and probably act 

 as the chemotactic substance.) Such a chemotactic attraction 

 may, rather than an electrokinetic one, be responsible for the 

 migration of leucocytes to a wound, or both may function. 



Cataphoresis in Protoplasm. — The cataphoresis of microscopic 

 granules suspended in the fluid protoplasm of cells was early 

 recorded by Carlgren and others. C. V. Taylor has succeeded in 

 demonstrating the cataphoretic migration of microscopic and 

 ultramicroscopic granules in the fluid protoplasm of a slime mold. 

 Dark-field illumination and an exceedingly weak direct current 

 applied through especially designed, and very minute, non- 

 polarizable microelectrodes were used. When the current was 

 applied, the ultramicroscopic particles migrated, some to the 

 anode and some to the cathode. A considerable group of the 

 particles, still in rapid Brownian movement, remained in the 

 center of the field and so were apparently electrically 

 neutral. 



