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. 2 



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, 3 in which the 



1 Abel, Mrs. Mary Hinman, "Care of Food in the Home," Farmers' Bul- 

 letin 575, U.S. Dept. Agr., 1909. 



3 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. 



" Directions for the Home Pasteurization of Milk," Circular 162, Bureau 

 of Animal Industry, U.S. Dept. Agr., 1912. 



