t of
hairs, epithelial scales and masses of dirt and filth, but during the
milking process, as at all other times, every motion of the animal is
accompanied by a shower of _invisible_ particles more or less teeming
with bacterial life.

The amount of actual impurities found in milk is often considerable and
when it is remembered that about one-half of fresh manure dissolves in
milk,[24] and thus does not appear as sediment, the presence of this
undissolved residue bespeaks filthy conditions as to milking. From
actual tests made, it is computed that the city of Berlin, Germany
consumes about 300 pounds of such dirt and filth daily. Renk has laid
down the following rule with reference to this insoluble dirt: If a
sample of milk shows any evidence of impurity settling on a transparent
bottom within two hours, it should be regarded as too dirty for use.

While the number of organisms here introduced is at all times large, the
character of the species is of even greater import. Derived primarily
from dirt and fecal matter, it is no wonder that such forms are able to
produce very undesirable fermentative changes.

~Influence of milker.~ The condition of the milker is not to be ignored in
determining all possible factors of infection, for when clothed in the
dust-laden garments that have been worn all day, a favorable opportunity
for direct contamination is possible. The filthy practice of wetting the
hands with milk just before milking is to be condemned. The milker's
hands should be washed immediately before milking in clean water and
dried. A pinch of vaseline on hands is sometimes used to obtain a firmer
grasp and prevents the ready dislodgment of scales.[25] It must also be
borne in mind that the milker may spread disease through the milk. In
typhoid fever and diphtheria, the germs often remain in the system for
weeks and thus make infection possible. Stocking[26] has shown that the
individual milker exerts a potent influence on the total germ content of
milk, even where the procedure is quite the same. In sanitary dairies
milkers are usually clad in white duck suits.

~Milking by machinery.~ Several mechanical devices have been invented for
milking, some of which have been tested bacteriologically as to their
efficiency. Harrison[27] has examined the "Thistle" machine but found a
much higher germ content than with hand-drawn milk. The recent
introduction of the Burrel-Lawrence-Kennedy machine has led to numerous
test