358        DISINFECTANTS  IN  ARRESTING  CATTLE  PLAGUE. 
glands,  &c. ;  the  breath,  perspiration,  and  excreta  of  the  animals 
forming  vehicles  for  the  distribution  of  the  virus.  By  "  living  " 
cells  is  not  meant  living,  in  the  sense  in  which  an  animal,  or  even 
a  low  form  of  infusoria,  lives  ;  but  living  as  a  seed,  or  as  vaccine 
matter,  even  when  dried,  may  be  living,  inasmuch  as  it  still  pos- 
sesses reproductive  vitality. 
6.  It  is  by  no  means  certain  that  the  multiplication  of  these 
individual  cells  is  the  immediate  cause  of  the  blood  poisoning. 
The  analogy  of  the  action  of  virus  on  the  blood  to  that  of  yeast 
on  sugar  renders  it  more  probable  that  this  is  not  the  fact.  In 
the  case  of  the  best  known  ferment — yeast — its  cells  multiply  by 
feeding  upon  the  sugar  in  the  liquid ;  alcohol  and  carbonic  acid 
being  their  excretions.  It  is  therefore  probable  that  during  the 
multiplication  of  the  virus  cells,  they,  in  a  similar  manner,  im- 
poverish and  weaken  the  blood,  by  feeding  upon  some  element 
in  it,  whilst  at  the  same  time  they  excrete  a  poison  to  which  the 
symptoms  of  the  disease  may  be  immediately  due. 
7.  The  foregoing  view  differs  from  the  prevalent  notion  that 
the  virus  of  contagion  consists  of  decomposing  organic  matter, 
declining  from  a  complex  towards  a  more  simple  chemical  con- 
stitution, and  during  its  degradation  inducing  decomposition  in 
the  neighboring  particles  of  matter.  This  chemical  theory  at 
first  sight  appears  very  plausible ;  but  it  fails  to  satisfy  one 
necessary  condition  of  the  present  case.  It  is  possible  to  imagine 
that  the  force  set  free  in  the  declension  of  a  complex  chemical 
molecule  to  a  more  simple  form  will  be  sufficient  to  raise  a 
neighboring  molecule  to  a  structure  almost  as  complicated  as  the 
original ;  but  according  to  this  view  the  ferment  would  be  con- 
stantly diminishing,  whereas  in  reality  it  constantly  increases  in 
bulk.  The  hypothesis  is  therefore  insufficient  to  explain  the 
prodigious  procreative  power  of  the  original  particle.  This 
power  belongs  only  to  the  nature  of  an  organized  germ,  capable 
of  producing  multiples  of  itself  by  a  process  of  nutrition  and 
subdivision.  Thus  the  line  of  demarcation  between  organic 
poison  and  organized  virus  appears  to  be  very  clearly  defined. 
This  necessarily  brief  outline  of  the  theoretical  views  which 
have  governed  me  in  the  present  investigation  will,  it  is  hoped, 
be  clearer  and  more  intelligible  after  perusing  the  experimental 
