ORGANIC  MATTER  OF  THE  AIR. 
449 
fields,  producing  the  unhealthy  season,  I  do  not  doubt  that  the 
amount  will  be  much  higher.  It  was  not  convenient  for  me  to 
stay,  nor  to  go  further  to  places  distinctly  infected  with  malaria. 
I  was  desirous  of  trying  it  in  some  of  the  hovels  of  the  Vallois 
and  the  Yal  d'Aosta,  but  the  weather  being  fine,  and  the  people 
living  much  out  of  doors,  the  inquiry  was  not  encouraging.  The 
few  experiments  made  did  not  give  very  striking  results,  whereas 
the  lower  parts  of  our  own  towns  gave  results  most  decided.  I 
imagine  the  cause  of  this  to  be  that  a  drier  air  does  not  allow 
the  offensive  matter  to  rise  so  readily.  This  fact  has  many 
ramifications,  but  it  will  explain  several  difficulties  in  our  sani- 
tary science.  It  is  with  the  assistance  of  moisture  that  the 
organic  matter  is  conveyed  into  the  air. 
Moisture  itself,  as  may  be  supposed,  does  not  produce  any  ac- 
tion on  the  test ;  one  of  the  lowest  numbers  obtained  was  on  the 
German  Ocean,  about  60  miles  from  land;  the  day  was  calm  and 
clear.  In  the  straits  of  Dover,  when  the  wind  was  blowing 
briskly  from  the  German  Sea,  the  amount  obtained  was  very 
high,  but  as  there  was  a  slight  spray  the  experiments  were  dis- 
regarded. About  8000  feet  high  on  the  Alps,  a  dense  fog 
showed  also  one  of  the  smallest  amounts  obtained ;  the  ground 
was  entirely  bare  rock,  and  could  not  give  out  organic  matter. 
The  amount  was  2-8. 
The  influence  of  height  was  very  decided ;  in  the  higher 
grounds  of  Lancashire,  near  Preston,  the  numbers  being  from  2 
to  4.  A  wind  blowing  down  from  the  Mer  de  Glace  gave  rather 
more  than  at  a  lower  point,  although  coming  down  the  hill;  a 
dry  pine  forest  in  the  neighborhood,  although  very  fragrant,  did 
not  appear  to  raise  the  number.  The  influence  of  the  sea  and 
of  height  seem  equally  decided. 
A  few  hasty  experiments  made  in  the  hothouses  at  Kew  led 
me  to  believe  that  there  was  less  increase  there  than  might  have 
been  expected,  the  amounts  obtained  being  less  than  in  London, 
but  more  than  outside  the  houses,  where  it  was  cooler.  At  the 
same  time  weeks  or  months  should  be  given,  when  only  hours 
were  allowed  for  the  experiments. 
The  influence  of  heat  appears  to  be  to  increase  the  amount, 
when  there  is  moisture  present. 
