which  was  placed  in  a  second  larger  beaker,  surrounded  by  cotton 
wool  and  supported  on  cork.  Between  the  two  beakers  an  air  space 
existed,  as  shown  in  Fig.  i.  A  thermometer  dipped  into  the 
ammonium  nitrate  mixture  was  used  for  stirring  up  the  solid  salt 
from  time  to  time  as  required.  In  this  way  the  temperature  of  the 
mixed  plasma  and  red  cells  was  kept  at  o°  C.  to  5°  C.  If  desired  a 
temperature  below  0°  C.  could  have  been  maintained.  The  time 
elapsing  between  collecting  and  centnfugalising  the  blood  was  in 
most  cases  about  six  minutes  ;  that  between  pipetting  off  the  plasma 
and  cooling  it  in  the  freezing  mixture  was  generally  about  twenty 
minutes  to  two  hours.  While  in  the  freezing  mixture  the  red  cells 
were  once  or  twice  distributed  in  the  plasma  by  stirring  with  a 
capillary  glass  rod.  After  being  kept  in  the  freezing  mixture  for 
half  an  hour,  the  tube  containing  the  plasma  and  red  cells  was  put 
for  three  hours  in  an  incubator  kept  at  37°  C.,  the  red  cells  being 
stirred  from  time  to  time  with  a  glass  rod  as  before. 
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I'lG.  I.  Apparatus  employed  for  testing  haemolytic  property  of  blood 
plasma. 
