150 AGRICULTURE. 



Some of them are acting constantly in the soil, changing some 

 of the humus into nitrates for the roots of plants. Some of 

 them gather on cheese and form blue-mold. Some of them 

 get into the refuse barrels and cause decay of the pieces of 

 food thrown therein. Some of them drop into the cider or 

 wine and make vinegar. There are very many kinds, each 

 kind working in its own way. They 

 can De recognized only by a very power- 

 ^ u ' microscope. One kind, that is 

 very common, drops into the milk 

 anc ^ changes the sugar into lactic 

 acid. Supposing that we do not 



Fig. 80. One of the ferments ? 



of mi.k, magnified. clean out a milk pail or a milk 



can thoroughly, what will happen? Many of these little 

 ferments, or bacteria, as they are called, will settle on the sides 

 and get into the cracks, and just as soon as milk is placed in 

 the vessel they will begin to act upon the milk, causing it to 

 sour rapidly, or to produce substances that have a nasty taste 

 or an unpleasant odor. If there is any trace of milk left in 

 the can after the milk is poured out, they rush down upon it 

 and begin to feed and increase in number. Any dirty places 

 about the floor, or table, or walls, will also cause them to greatly 

 increase. Tainted milk is not pleasant to drink, it makes poor 

 butter and poor cheese ; so that for success in dairying every- 

 thing must be kept clean, very clean the cows, the food, the 

 stables, the pails, the utensils, the milk house, and the dairy 

 workers. One of the great reasons for using ice and cold 

 spring water to keep the milk, cream, and butter sweet is 

 because these little ferments cannot do harm in very cold 

 places. They do their work only when they are kept moder- 

 ately warm. Science, then, teaches us that in dairying it pays 

 to be clean. In addition to ferments which may get in from 

 the outside it is thought that there are minute forms of life some- 

 what similar to these ferments, which are contained in the 



