Microorganisms in Relation to Man 579 



tained more than five thousand. Bacteria have strong domestic 

 tendencies, abounding in close association with mankind. 



In all surface water, as in springs, wells, brooks, rivers, lakes, 

 and oceans, bacteria of certain kinds are present. Stagnant 

 water is very favorable to them. Water into which sewage is 

 emptied contains not only the usual species and numbers, but 

 many forms which come from infected persons and are therefore 

 dangerous to human life and health. When shellfish, such as 

 oysters, clams, and others, occupy such contaminated waters 

 and are used for food, they are a source of danger. 



All kinds of food materials may be infested with bacteria. 

 Milk, even when the strictest sanitary precautions are taken 

 in milking and handling, is alive with them. They are collected 

 from the air, the body of the cow, the milk vessels, and the 

 persons handling the milk. The varieties collected are many, 

 some useful and others useless, and possibly others harmful or 

 disease-causing, as those introduced by a typhoid fever carrier 

 in handling milk. Blue or otherwise colored milk, sour, curdling, 

 " slimy" milk are caused by the activities of different kinds 

 of bacteria. How such changes may be retarded and dan- 

 gerous bacteria destroyed will be taken up later. Other food 

 materials may have a large allotment. Eggs just beyond the 

 point of freshness, meats that have become tender with storage, 

 vegetables and fruits of all sorts, these have their freight of 

 bacteria. Moldy bread and cake are alive with them. But it is 

 not necessary that foods should be tainted or discolored to 

 prove the presence of the microorganisms. Food products 

 purchased in the market and sold as edible show astonishingly 

 large numbers of bacteria. One sample of catsup showed by 

 count over 5,000,000 bacteria to the cubic centimeter. Another 

 revealed 400,000,000 bacteria and 7,500,000 spores per cubic 

 centimeter. A plum jam had half a million bacteria and as 

 many yeasts per cubic centimeter. The number of bacteria 

 and other organisms in any food is definitely related to thf 

 cleanliness of the place where it is prepared. 



