42 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
therefore proposed the FM-reductase test as a means of 
determining whether or not a cow is “fresh.” FM- 
reductase is absent, or present only in very small quan- 
tity, in the first milk drawn at a milking, but it is always 
present in the end milk. After stasis of milk, it is absent. 
The reaction cannot be used for the detection of mastitis, 
because while reduction occurs rapidly in some cases, in 
others it occurs more slowly than in normal milk or may 
not occur at all. 
Antibodies or Immune Bodies.—Antibodies are sub- 
stances which are produced in the animal body to pro- 
tect it from the action of bacteria or their toxins. ‘The 
term includes antitoxins, agglutinins, precipitins, op- 
sonins, lysins (amboceptors) , complement, etc. Comple- 
ment is always present in the blood and the other kinds 
of antibodies are also contained in the normal serum in 
a non-specific form, but these antibodies do not appear in 
the blood in a specific form until after the body is invaded 
by pathogenic organisms or their toxins. 
It has been demonstrated that antitoxins, agglutinins, 
and opsonins pass over from the blood into the milk when 
the udder is in a normal condition. Bacterio-lysins are 
eliminated in the milk when the udder is affected with 
mastitis and during the colostral stage, but it is doubtful 
if they pass over from the blood into the milk under nor- 
mal conditions at other times. Complement is present 
in colostrum and also in milk when the udder is affected 
with mastitis. It may be present in normal milk for as 
long as twenty-six days after parturition, but after that 
time it is absent, according to some observers. The com- 
plement demonstration test has not come into general 
use for the detection of mastitis principally because cer- 
