60  Comparative  Composition  of  Milks.  {^ebruaryffg™' 
Harrington  and  Kinnicutt  themselves  obtained,  as  they  report, 
7  97  per  cent,  of  carbonic  acid  gas  after  incinerating  the  salts  of 
human  milk,  and  yet  no  statement  is  made  of  the  presence  of  any 
organic  acid  salts. 
With  reference  to  the  Soldner  analysis,  it  should  be  noted  that 
while  the  citrates  embrace  one-third  of  the  salts,  the  chlorides 
approximate  nearly  one-fifth,  and  the  phosphates  nearly  one-half. 
The  ash  of  the  milk  does  not  represent  the  salts  of  milk  in  the  form 
in  which  they  occur  in  milk  ;  it  represents  only  the  incinerated  salts, 
the  incineration  destroying  all  organic  matter  and  altering  the 
chemical  form  of  the  salt. 
PERCENTAGE  COMPOSITION  OF  COWS'  MILK  DURING  THE 
PERIOD  OF  LACTATION.     (Farrington,  quoted  by  Chapin) 
Number  of 
Samples 
Fat 
Proteids 
278 
428 
614 
Minimum,  1.50 
Maximum,  6.60 
Minimum,  2.50 
Maximum,  7.90 
Minimum,  2.90 
Maximum, 12. 30 
Minimum,  2.64 
Maximum,  4.11 
Minimum,  2.92 
Maximum,  3.89 
Minimum,  2.98 
Maximum,  5.30 
Cow's  milk,  like  human  milk,  varies  in  composition  during  the 
act  of  suckling  or  milking.  Thus,  as  Leach  reports,  the  "  fore-milk" 
of  cows  contains  from  1-07  to  1-32  per  cent,  of  fat,  and  the  "strip- 
pings  "  from  9  63  to  10-36  per  cent,  of  fat,  while  the  non-fatty  solids 
range  in  the  44  fore-milk"  from  IO-20  to  10-51  per  cent.,  and  in  the 
"  strippings  "  from  9-27  to  9-55  per  cent. 
It  should  be  observed  also,  as  Farrington  shows,  that  cow's  milk 
varies  in  composition  during  the  period  of  lactation,  and  the  milk 
of  a  mixed  herd  is,  therefore,  much  more  uniform  than  the  milk  of 
a  single  cow,  because  the  milk  of  cows  for  calves  of  different  ages  is 
mixed,  and  the  minimum  and  maximum  percentages,  due  to  the 
individual  factor,  are  equalized.  And  so,  when  large  numbers  of 
analyses  are  added  together  and  averaged,  the  individual  differences, 
which  are  sometimes  extreme,  become  equalized  in  the  general 
averages. 
