In general, these measures closely parallel those provided  for  defense  against  chemical  attack. Since the inhalation of airborne organisms is considered to be the greatest potential hazard in biological   warfare,   the   protective   mask   is   an important component of defensive equipment. A mask  that  is  in  good  condition  and  has  been properly fitted will greatly reduce the possibility of  inhaling  infectious  material  in  the  air.  Since the  individual  cannot  detect  the  presence  of biological agents, the use of the mask and other protective   equipment   will   depend   upon   early warning. To  produce  disease,  biological  agents  must gain  entrance  into  the  body.  A  concentration  of biological  agents  on  the  skin  might,  in  time,  be transferred  to  a  portal  of  entry.  Any  type  of clothing will provide some protection by reducing the quantity of agents coming in contact with the skin.  The  degree  of  protection  afforded  is dependent  upon  how  well  the  fabric  stops penetration and the number of layers of clothing being worn. Since this protective effect is due to the  mechanical  filtering  or  screening  action  of the  cloth,  it  is  important  that  shirt  and  jacket collars be fastened, sleeves rolled down and cuffs buttoned,   trouser   cuffs   stuffed   inside   tops   of boots  or  socks,  and  all  other  garment  openings tied or otherwise secured to minimize the entry of  airborne  organisms  and  to  reduce  the  risk  of bodily contact with biological agents that may be present  on  the  surface  of  the  ground  or  in  the air. Military  headgear  helps  safeguard  the  hair from  heavy  contamination,  and  ordinary  gloves or mittens provide protection for the hands. The impregnated  type  of  clothing  issued  for  protection against chemical agents provides a higher degree of  protection  than  the  ordinary  uniform,  and whenever it is available it should be used. Upon notification of an attack with biological agents,  or  before  entering  an  area  known  to  be contaminated  by  them,  the  individual  will: Put  on  protective  mask  and  check  it  for correct  fit. Button   clothing.   Tie   clothing   at   wrists and ankles with string or extra shoelaces. Put   on   special   protective   clothing,   if available. Put  on  gloves,  if  available. While in the contaminated area, maintain the  provisions  outlined  above. .   Upon   leaving   the   area,   proceed   with decontamination  measures  to  the  extent the situation permits. GROUP  PROTECTION In  biological  as  well  as  in  chemical  and radiological warfare, a tightly constructed shelter offers  great  protection.  The  shelter  must  be pressurized  to  prevent  entrance  of  the  micro- organisms, which is accomplished by introducing filtered  air  into  the  shelter.  If  the  shelter  is reasonably  tight,  this  incoming  air  will  cause any  flow  of  air  to  be  outward.  Any  building, shelter, or field fortification without this feature provides  only  limited  protection  from  aerosols. Eventually  microorganisms  will  penetrate  through cracks  and  will  constitute  a  respiratory  hazard unless   the   protective   mask   is   worn.   Again, utilization  of  shelters  will  depend  upon  early warning. PROTECTION  OF  FOOD  AND  WATER Food  and  water  supplies  are  especially susceptible to deliberate contamination. Civilian supplies all too frequently do not receive careful supervision  and  protection  and  must  always  be suspected of accidental or deliberate contamina- tion. It should also be emphasized that water is not  necessarily  pure  just  because  it  comes  from a  faucet.  In  some  countries  pure  water  is  the exception rather than the rule. The safest rule is to consume only foods and drinks received from military sources. Procedures for protection of the water  supply  and  routines  for  inspection  and decontamination are well defined in the military and,   if   diligently   observed,   will   protect   from deliberate  contamination. Water Chlorination  is  by  far  the  almost  universal method of purifying water, and it destroys most of the biological agents. Boiling maybe required to ensure proper decontamination in exceptional cases. The  military  establishes  water  points  in  the field whenever possible. The equipment location at these points provides for filtration as well as chlorination   and,   when   properly   operated,   is effective   in   removing   organisms   that   produce disease.  Some  biological  agents  cannot  be destroyed   by   normal   water   purification   tech- niques.  When  biological  agents  are  known  to  have been used, all drinking water must be boiled. In 6-4