1 82 ELEMENTARY BIOLOGY 



capable of eating small particles by swallowing them into the 

 protoplasm of which they consist, just like the ameba and other 

 one-celled animals. 



These ameba-like corpuscles are found in the blood not only 

 of mammals but of all animals that have blood ; and they are 

 very much alike in all, so far as general appearance and be- 

 havior are concerned. Their function has come to be under- 

 stood only in modern times, chiefly through the works of the 

 Russian biologist Elie Metchnikoff, the late director of the 

 Pasteur Institute in Paris. 



To help us understand the functions of these cells it is 

 well to recall that whereas the one cell of the ameba carries 

 on all the functions of a living body, the various cells of a 

 many-celled animal like a butterfly or a baby are differentiated 

 in regard to function as well as in regard to structure. Now, 

 the white corpuscles are in many ways the least differentiated 

 cells in the body. They are the ones that have the general 

 qualities of protoplasm in the greatest degree ; they have not 

 become specialists in any one line. They can move, like 

 muscle cells, but not so quickly or so vigorously. They are irri- 

 table, like nerve cells, but in a slighter degree. They are 

 chemical laboratories, like gland cells, but do not produce 

 specialized juices. They are digesting cells, and so on. 



With this view of the white corpuscles as undifferentiated, 

 wandering cells we may try to understand just what they do 

 in the body. 



1 . As eating-cells (called by Metchnikoff phagocytes, which 

 means " eating-cells ") they are capable of engulfing foreign 

 particles with which they may come in contact. In this manner 

 they may eat and digest dead particles resulting from the break- 

 ing down of tissue cells, and live cells introduced from without 

 that is, bacteria that may get into the body in various ways. 



2. As sensitive or irritable cells they may respond to a 

 chemical stimulation by producing substances that neutralize 

 or counteract foreign chemicals, as various kinds of poisons. 



