380 PROTOPLASM 



pollen grains. The charge in every case is negative. Here and 

 there in the literature, one reads that certain cells are positively 

 charged or that certain cells appear to be positive at times and 

 negative at other times. Most results that indicate a positive 

 sign of the charge on living cells are erroneous in so far as they 

 are due to one of two very common faults in cataphoretic research 

 work, viz., failure to observe the level at which movement takes 

 place and failure to measure pH. The strong electroendosmotic 

 flow of the water in a cataphoretic chamber may cause a weakly 

 charged negative particle to travel to the negative pole against 

 its own electrokinetic attraction for the positive pole. Acidity 

 is another source of error. Acid added to a suspension of electro- 

 negative bacteria may reverse the charge at reactions on the 

 alkaline side of their isoelectric points. That colloidal particles 

 may change sign when salt or acid is added has been seen. The 

 change usually occurs at an abnormally low (or high) isoelectric 

 point, i.e., at a salt concentration or pH value unlikely to occur 

 in nature. Should a cell have an isoelectric point near neutrality, 

 then the possibility of its being either negative or positive in the 

 natural state would have to be granted, but as yet there is little 

 evidence that living cells are positively charged in their normal 

 environment. Comandon has observed red blood cells migrating 

 to the anode (the cells therefore are negative) and trypanosomes 

 migrating to the cathode (and therefore positively charged). 



Spermatozoa and Spirochaeta are cells that have most often 

 been reported to be positively charged. Why they should be 

 so it is difficult to understand. Koltzov and Schroder found 

 that some of the spermatozoa of rabbits are negative, some 

 positive, and some show no migration in an electric field. They 

 believe that difference in sign of charge may be associated with 

 chromosome and sexual characters. In order to put all such 

 data to the test of modern and precise technique, S. Mudd studied 

 the sperm from man, bull, ram, rat, rabbit, and guinea pig and 

 found it in every case to be negative. He also applied the 

 same careful methods to spirochaetes (bacteria) which had been 

 described as positively charged. These, too, he found to be 

 negative. 



Katsuma Dan, working on the eggs of the sea urchin and 

 using a special technique because of the large size of the eggs 

 when compared to colloidal particles, found the charge of unferti- 



