108 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
numbers in the sediment and cream, especially the poly- 
morphonuclear leucocytes in purulent catarrh. The 
catalase content is increased. Coagulation occurs when 
the alcohol or the boiling test (see pages 284, 285) is 
applied. 
On account of the difficulty of detecting catarrhal 
mastitis in its early stages, the determination of the leuco- 
cytic content of samples of market milk has sometimes 
been relied on to discover the presence of the disease. It 
has been demonstrated that cases of catarrhal mastitis 
may be detected by this method but we have no means of 
knowing how many of such cases escape discovery; there 
is reason to believe that many are overlooked. The ex- 
amination of samples of milk from individual cows by 
means of the catalase test is the most efficient method of 
detecting the disease (see page 287). When numerous 
very small, punctiform, brownish colonies appear in the 
plates prepared for determining the number of bacteria in 
milk and these are found upon microscopic examination to 
consist of streptococci in long chains, an examination of 
the herd will usually discover the presence of one or more 
cases of catarrhal mastitis. 
A special form of purulent catarrhal mastitis which 
leads to multiple abscess formation is caused by the Bacil- 
lus pyogenes. The secretion has afoul odor. The disease 
occurs most commonly in “ dry ” cows, but is usually not 
discovered until they become “ fresh.” 
2. Parenchymatous Mastitis—The detection of this 
form of mastitis offers no difficulties to the dairy inspec- 
tor. It is attended with an immediate and pronounced 
swelling of the affected portion of the udder and the milk 
at once presents marked changes. As the name indicates, 
it is an inflammation of the alveoli and small tubules of 
