368  Physiological  Characteristics  of  Acetylene.  { A^Ugu"t'  SE**' 
from  the  tube;  and  (b)  a  gas-sampling  tube.  Collections  were  made 
over  mercury  and  analysis  was  made  over  mercury  in  a  Hempel 
apparatus.  The  cabinet  was  tightly  built,  but  not  sufficiently  so 
to  prevent  escape  of  air  sufficient  to  equalize  the  pressure  without 
and  within  the  cabinet  when  gas  was  introduced.  A  movable  electric 
fan  within  the  cabinet  was  adapted  to  produce  motion  of  the  air. 
When  carbon  dioxide  was  mixed  with  atmospheric  air,  it  was 
noted  that  such  mixture  produced  an  increased  rate  of  respiration, 
even  when  the  proportion  of  carbon  dioxide  was  small.  Rabbits 
and  guinea-pigs  showed  a  marked  increase  when  as  much  as  4  to  5 
per  cent,  of  carbon  dioxide  was  present.  With  increasing  proportions 
respirations  became  deep  and  labored,  frequently,  as  was  observed 
in  guinea-pigs,  reaching  a  condition  of  diaphragmatic  spasm.  Loss 
of  muscular  power  developed  so  that,  with  guinea-pigs,  ability  to 
support  the  body  was  lost  when  the  carbon  dioxide  reached  20  to  25 
per  cent.  These  symptoms  developed  irrespective  of  whether  lamps 
were  burnt  in  the  same  atmosphere.  With  rabbits,  when  lamps 
were  burning,  loss  of  muscular  power  appeared  with  the  same  pro- 
portion of  carbon  dioxide  as  with  guinea-pigs,  but  in  a  single  obser- 
vation made  without  lamps,  the  loss  of  power  appeared  when  the 
carbon  dioxide  had  reached  36  per  cent.  No  effort  was  made  to 
determine  the  percentage  of  carbon  dioxide  that  would  produce  death, 
as  it  was  believed  that  the  proportion  producing  loss  of  muscular 
power  represented  the  limit  of  possible  tolerance.  It  may  be  noted, 
however,  that  in  the  experiment  carried  to  36  per  cent,  carbon  dioxide, 
the  rabbit  quickly  recovered,  two  guinea-pigs  recovered  somewhat 
slowly,  and  one  guinea-pig  died,  when  the  animals  were  removed 
into  fresh  air.  Thus  it  appears  that  even  with  guinea-pigs,  the  fatal 
carbon  dioxide  proportion  is  not  much  if  any  below  36  per  cent, 
while  the  carbon  dioxide  warning  point  is  not  above  4  to  5  per  cent., 
To  test  the  effect  of  carbon  dioxide  on  man,  ioJ/2  cu.  ft.  of  carbon 
dioxide  were  passed  into  the  cabinet,  when  a  young  man  entered,  the 
door  being  opened  for  that  purpose  and  quickly  closed.  After 
entering,  the  fan  was  started.  The  rate  of  respiration  at  once  rose 
from  18  to  48,  being  deeper  and  labored.  He  almost  immediately 
complained  of  feeling  dizzy.  At  the  end  of  2^  min.  there  was  a 
feeling  of  impending  loss  of  consciousness.  A  sample  of  the  air 
mixture  was  at  once  taken  and  at  the  end  of  3  min.  the  man  came 
out.  His  respiration  quickly  returned  to  normal,  but  his  face  was 
flushed  and  he  complained  for  several  hours  of  a  slight  frontal 
