Safeguards against Disease 149 



the leucocytes do not cease to be leucocytes 

 when they become phagocytes, any more 

 than a son of Erin ceases to be an Irishman 

 when he becomes a plumber. 



The leucocytes, as well as some other body 

 cells, have the further useful capacity of 

 secreting and under certain conditions setting 

 free, such chemical substances in solution 

 as dissolve refractory tissues, dead bone, for 

 example, and so clear the ground for new 

 growth. 



Thus far we have been considering harmful 

 stuff in the body, such as poisons and dead 

 particles, and the ways in which the body 

 protects itself against them. Now let us 

 look at some more striking aliens, themselves 

 alive, which often intrude upon the balanced 

 life of the healthy man. 



The presence of bacteria in the body is of 

 varying significance, depending upon where 

 they are and what their pedigree. The healthy 

 skin keeps out most of them. The ever 

 swinging cilia in the windpipe sweeps them 

 out in hosts. In the mouth and nose many 

 are destroyed, but many lead here a placid, 



