probably  a  low  estimate,  we  obtain  a  total  of  7,845  days  lost  in  actual 
service  during  the  two  years. 
Spleeji  Rate. 
These  various  figures,  the  death-rate  from  malaria,  and  the 
Hospital  admission  rate,  give  of  course  only  an  approximate  idea  of 
the  prevalence  of  malaria  in  a  community,  that  is  to  say,  of  the 
number  of  infected  persons  in  a  locality.  But  it  is  obvious  that  a 
very  large  number  of  individuals  will  not  be  included  in  statistics 
derived  from  such  sources.  A  great  many  people  suffer  from  malaria 
and  recover,  and  a  large  proportion  of  these  receive  no  hospital 
treatment.  It  is  evident,  then,  that  the  percentage  of  infected  people 
must  be  very  much  larger  than  has  been  shown.  The  only  absolutely 
accurate  method  of  determining  the  exact  proportion  of  infected 
individuals  in  the  general  population  would  be  to  examine  the  blood 
of  a  very  large  number  of  people,  taken  at  random  from  the  general 
population,  for  malarial  parasites,  and  this  would  give  us  what  has 
been  termed  by  Christopher  and  Stephens  the  ‘endemic  index’  of 
malaria.  Such  a  process  of  microscopic  examination  is,  however,  a 
very  laborious  one,  and  occupies  a  very  large  amount  of  time,  as 
parasites  are  frequently  very  difficult  to  detect,  and  consequently,  this 
method  is  one  which  it  is  rarely  possible  to  adopt. 
But  there  is  a  method  which  gives  a  very  fair  indication  of 
malaria  in  a  locality,  and  which  was  first  put  in  practice  by  Professor 
Ross  in  a  comprehensive  manner  in  connection  with  his  recent  visit 
to  Mauritius.  This  depends  upon  the  fact  that  malaria  causes  an 
enlargement  of  the  spleen,  and  consequently  the  number  of  people 
with  enlarged  spleens — what  Professor  Ross  calls  the  ‘  spleen  rate  ’ — 
IS  a  fairly  reliable  index  of  the  amount  of  malaria  in  a  locality,  for 
apart  from  Kala-azar,  which  so  far  as  I  know  is  non-existent  in 
Jamaica,  malaria  is  the  only  endemic  disease  which  causes  a  chronic 
enlargement  of  the  spleen. 
And  it  has  been  proved  that  in  a  locality  where  malaria  is 
endemic,  children  up  to  the  age  of  fifteen  or  sixteen  suffer  to  a  large 
extent  from  enlarged  spleen,  while  over  that  age  it  appears  to 
diminish  in  size,  and  is  less  easily  detected.  In  other  words,  the 
native,  as  he  grows  older,  appears  to  acquire  a  certain  degree  of 
