190 Studies in Animal Behavior 



Among the most motile of the cells of the body 

 are the leucocytes or white blood corpuscles. These 

 cells are very much like Amoebae in their appear- 

 ance and their activities. They have the property 

 of creeping about in the various spaces of the body 

 and of passing through the delicate walls of the 

 capillaries. Their power of engulfing bacteria and 

 fragments of broken-down cells is well known. They 

 act not only as the scavengers of the body, but by 

 virtue of their power of destroying bacteria they 

 defend the body against various disease germs that 

 constantly invade it. Apparently they are drawn 

 to centers of bacterial infection by^a sort of chemo- 

 taxis. This is shown by an ingenious experiment by 

 Massart in the following way: A tube of cul- 

 ture medium containing a culture of the bacterium 

 Staphylococcus pyogenes albus was introduced into 

 the abdominal cavity of a rabbit. After a time it 

 was found that the leucocytes had wandered into the 

 tube in large numbers. A similar tube filled with 

 the same medium but containing no bacteria was 

 also introduced, but it was not entered by the leu- 

 cocytes. It is probable, therefore, that some sub- 

 stances produced by the bacteria caused the leu- 

 cocytes to enter the tube. 



The species of bacterium used in the experiment 

 is one of the common forms that give rise to the 

 production of pus. This substance which so fre- 

 quently gathers in inflamed areas is produced mainly 

 by degenerated leucocytes which have accumulated 



