356 SCIENCE OF HOME AND COMMUNITY 



Directions, i. Pour 100 cc. of water into a flask and boil 

 for ten minutes. When the water cools add I cc. of milk and 

 shake thoroughly. 



2. Melt a tube of culture medium. Into this put one drop 

 of the diluted milk. Shake it thoroughly. Pour into a steril- 

 ized petri dish and cover. 



3. Allow to stand for several days and count the number of 

 colonies. Each colony started from one bacterium. Estimate 

 the number of bacteria in I cc. of the undiluted milk, re- 

 membering that about 15 drops make a cubic centimeter and 

 that i cc. of the milk was diluted with 100 cc. of water. 



4. Prepare several tubes and dishes, putting in milk from 

 different sources. Also take milk from the same sample after 

 it has stood for a day, because the number of bacteria depends 

 on the age of the milk. 



Foods. Most of our foods are bought from public sup- 

 plies, so that it is not possible for each individual to deter- 

 mine for himself the conditions under which foods have been 

 prepared. It is necessary, therefore, to have these matters 

 controlled by laws, and foods examined by men who make it 

 a business to inspect them. 



Diseased foods. In order to know how best to protect 

 our food, we must first know what some of the impurities 

 are that are found in foods. Foods may be diseased or 

 decayed. For example, if cattle that have had tubercu- 

 losis are killed and sent to market, the meat contains the 

 germs and is dangerous as a food. In the preparation and 

 marketing of foods, they may be contaminated with germs 

 through exposure to dust and flies or by being handled by 

 people who are diseased. Food may be kept so long before 

 being sold to the consumer that it begins to decay; then 

 there are formed certain poisons called ptomaines, which 

 often cause serious sickness and even death. 



Adulteration. Various kinds of adulterations are prac- 

 ticed but the three most commonly found are: first, the 



