PHYSICAL AGENTS 



141 



be taken that the burial is done in such a way that the sur- 

 face soil is not contaminated either directly or by material 

 brought up from below by digging or burrowing animals, 

 insects, worms or movement of ground water to the sur- 

 face. Also that the underground water supply which is 



Fig. 101. — Berkefeld filter candles about one-half natural size. 



drawn upon for use by men or animals is not contaminated. 

 Frequently infected material, carcasses of animals, etc., are 

 treated in some way so as to aid the natural process of 

 destruction of the organisms present, especially by the use 

 of certain chemical agents, as quicklime (see page 144). 



