DISINFECTANTS  IN  ARRESTING  CATTLE  PLAGUE.  357 
distances  in  clothing  or  running  water,  and  in  a  variety  of  ways 
incompatible  with  the  behaviour  of  gases.  For  these  reasons, 
and  many  others  unnecessary  to  adduce  here,  it  seems  clear  that 
the  disease  must  be  communicated  by  the  agency  of  solid,  non- 
volatile particles. 
4.  The  specific  disease-producing  particles  must,  moreover,  be 
organized,  and  possess  vitality  ;  they  must  partake  of  the  nature 
of  virus  rather  than  of  poison.*  No  poison  yet  known  to  chem- 
ists can  approach,  even  in  a  faint  degree,  the  tremendous  energy 
of  the  active  agent  of  infectious  diseases.  A  poison  may  be  or- 
ganic, but  it  is  not  organized.  It  may  kill  with  far  greater 
rapidity  than  the  virus  of  infection,  but,  unlike  this  virus,  it 
cannot  multiply  itself  in  the  animal  economy  to  such  an  extent 
as  to  endow  within  a  few  hours  every  portion  of  its  juices  with 
the  power  of  producing  similar  results.  A  virus,  on  the  con- 
trary, renders  the  liquids  of  an  infected  animal  as  virulent  as 
the  original  germ.  Strychnine  may  be  regarded  as  the  type  of 
a  poison,  and  vaccine  matter  as  the  type  of  a  virus. 
5.  Many  considerations  tend  to  show  that  the  virus  of  cattle 
plague  is  a  body  similar  to  vaccine  lymph,  and  consists  of  germ- 
inal matter,  or  living  cells,  possessing  physiological  individuality, 
which,  if  not  exposed  to  extremes  of  heat,  cold,  or  dryness,  are 
capable  of  preserving  their  activity  for  a  certain  time  outside  the 
living  organism,  of  adhering  to  material  objects,  and  of  being 
carried  from  one  place  to  another  by  currents  of  air  ;  each,  when 
introduced  into  the  blood,  requires  a  certain  time  (known  as  the 
period  of  incubation)  during  which  the  septic  germs  develope  and 
multiply,  until  they  have  so  far  poisoned  the  blood  that  the  ordi- 
nary symptoms  of  disease  become  manifest. 
The  blood  poisoning  thus  set  up  may  legitimately  be  called 
"  fermentation  ,"  it  is  a  decomposition  caused  by  the  act  of  nu- 
trition of  the  living  cell,  whereby  it  reproduces  in  incalculable 
numbers  the  specific  septic  germs  which  have  given  it  birth. 
These  gradually  infes^  the  blood  and  other  animal  liquids,  and 
as  the  disease  progresses  are  discharged  from  the  skin,  throat, 
*  The  words  virus  and  poison  are  generally  regarded  as  synonymous. 
It  would  be  more  convenient,  and  would  tend  to  promote  accuracy  of 
thought,  were  the  distinction  here  made  generally  adopted. 
