S Dairy Bacteriology. 



it possible to include all of these types in a general con- 

 sideration of the subject. 



Nature of bacteria. The vegetable kingdom to which 

 the bacteria belong consists of plants of the most vary- 

 ing size and nature. Those of most common acquaint- 

 ance are the green plants varying in size from those 

 not visible to the naked eye to the largest trees. An- 

 other class of plants known as fungi or fungous plants 

 do not contain chlorophyll, the green coloring matter, 

 but are usually colorless and, as a rule, of small size; 

 among them are included such forms as the mushrooms, 

 smuts, rusts and mildews, as well as the molds and 

 yeasts. The bacteria are closely allied to this latter 

 class. "When first discovered they were thought to be 

 animals because of the ability of some forms to move 

 about in liquids. 



The bacteria, like other kinds of living organisms, 

 possess a definite form and shape. They are the simpl- 

 est in structure of all the plants, the individual organ- 

 ism consisting of a single cell. The larger and more 

 highly organized forms of life are made up of many mi- 

 croscopic cells, and the life of the individual consists 

 of the work of all the cells. The bacteria are very com- 

 parable to the single cells of the higher plants and an- 

 imals, but in the case of the bacteria the single cell is 

 able to -exist apart from all other cells and to carry out 

 all of its life processes including reproduction. 



Forms of bacteria. With the multicellular organ- 

 isms much variation in form is possible, but with these 

 single-celled organisms the possible variation in form 

 is greatly limited. Three well marked types occur 

 among the bacteria: the round or coccus form (plural 

 cocci) ; the rod-shaped or bacillus (plural bacilli) : and 



