THE BACTERIA 209 
killed. If such completely sterilized food is hermetically sealed 
in vessels that have been similarly sterilized, it will not decay. 
It is difficult, but entirely possible, to thoroughly sterilize both 
food and sealing appliances so that absolutely no organisms 
will grow.1 Other methods of preservation by the introduction 
of chemicals (antiseptics) that prevent the growth of bacteria 
are sometimes used. These chemical preventives are poisons. 
If eaten in very small quantities, injurious results may not be 
immediately noticeable, but the use of these preventives is at- 
tended by constant danger. Milk, meats, and confections that 
are so preserved should always be avoided.? 
195. Preservation of milk and water supply. The relation 
of bacteria to milk and water supply is a subject of the great- 
est importance. A rather large number of harmless bacteria 
may often be found in reasonably pure milk and water, but 
careless handling of bottles and cans, or the use of tubercu- 
lous cows, may result in widespread disease. If milking is 
done through absorbent cotton or through several layers of 
cheesecloth, used as a cover for the milk pail, most of the 
impurities are caught in the strainers. Milk pails and ship- 
ping cans and milk bottles should always be sterilized before 
they are used. Milkmen who were otherwise fairly careful in 
their work have been known to rinse their pails and cans in 
polluted wells or streams. Bacteria which produce various 
kinds of disease have thus been distributed. Either milk or 
water may be sterilized by boiling, and may be kept sterile if 
placed in sterile vessels. Both, however, are better if they can 
be kept in a pure condition without sterilization. An efficient 
method of preserving milk is by pasteurization,® in which the 
1 Abel, Mrs. Mary Hinman, ‘‘ Care of Food in the Home,’’ Farmers’ Bul- 
letin 375, U.S. Dept. Agr., 1909. 
2 Sometimes in canned goods, stale meats, and other foods, poisonous sub- 
stances known as ptomaines are formed. It is supposed that they are pro- 
duced as secretions from bacteria, as results of chemical change or decay of 
such foods as meats and fruits, or even from the disorganization of some of 
the bacteria. 
8 * Directions for the Home Pasteurization of Milk,” Circular 152, Bureau 
of Animal Industry, U.S. Dept. Agr., 1912. 
