48 DUST AND ITS DANGERS. 



quality in the body juices which is quite in- 

 imical to their life, or by those vigilant phago* 

 cytes which we have noticed above or per- 

 haps in other ways which we do not yet know 

 any thing about. The germs which are swal- 

 lowed after being caught in the nose or mouth 

 from the inspired air, or swept up from the air- 

 tubes by the ciliated cells, are, for the most 

 part, soon deprived of life by the digestive 

 fluids. 



There is one species of bacteria which we 

 are to learn more about presently (the tubercle 

 bacilli) which, when they lodge in the tissues, 

 sometimes stimulate the cells near them which 

 multiply and build up a dense enclosing wall 

 about the intruding germs, so that these be- 

 come imprisoned in a little bag or sac in the 

 body, and can neither get away, nor spread, nor 

 do further damage. They are sometimes so 

 cut off from nutriment, that they die, or at 

 best sustain for some time, a poor and meagre 

 existence. (See Fig. 6, p. 69.) 



There are individual conditions of the body 

 in which it affords a most obstinate resistance 

 to the incursions that is, the growth of bac- 



