182 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
tion in regard to cleanliness being noted. Cement is the 
best material because it can be most readily cleaned, but 
smooth boards with tight joints, oiled or painted, will 
do fairly well for the walls and ceiling, although it is 
desirable to have the walls finished in cement for about 
four feet above the floor, especially in the room used 
for washing the milk vessels and utensils. The floor 
should always be constructed of cement. The lighting 
should also be observed. There should be a sufficient 
number of windows to furnish good light, and some good 
method of artificial lighting is also desirable. All win- 
dows and doors should be screened against flies. 
3. Apparatus.—The apparatus present in the milk 
house and its condition should be observed. There ought 
to be some means of cooling the milk and keeping it 
cool, and there should be facilities for cleaning the milk 
vessels and utensils, including a convenient and plenti- 
ful supply of hot and cold water. If the milk is bottled, 
a bottle washer, bottle filler, and bottle capper should 
be provided. These need not necessarily be expensive. 
A sterilizer is also desirable. It is a protection against 
the contamination of the milk through returned bottles 
and it is also a great aid in keeping the milk vessels and 
utensils clean. A bottle filler and capper will guard 
the milk against contamination by the fingers. 
A cooler, sometimes called an aérator, is necessary 
for the rapid cooling of milk. This apparatus is con- 
structed so that the milk flows in a thin layer over a 
sheet of tinned metal while cold water or brine flows 
on the other side of the metallic sheet and absorbs heat 
from the milk. There are four types of milk coolers: 
(a) conical, ( b) corrugated, (c) tubular, and (d) inter- 
nal or double-tube. 
