2 MODERN DAIRY PRACTICE. 



Before proceeding to the consideration of these problems 

 it will, however, be necessary to give some general informa- 

 tion concerning bacteria and their prominent characteristics 

 of life, so that the reader will be able to follow the discus- 

 sions entered upon in the main part of this work. 



Bacteria. Bacteria are the tiniest forms of organic life 

 known; they are single cells belonging to the lowest type 

 of plant life. 



They vary somewhat in form and there is considerable 

 difference in size. The different species of bacteria cannot 

 be distinguished by their form and shape as with the 

 higher order of plant or animal life, because so many of 

 them have such strong similarities in this respect. The 

 usual method of classifying them, which is admitted to be 

 imperfect, bases the distinguishing characters entirely upon 

 shape. 



There are three fundamental types known, that may 

 be compared in shape to a ball, a short rod, and a cork- 

 screw. These three types are called (1) coccus, (2) ba- 

 cillus, and (3) spirillum. All forms of bacteria may be 

 referred to these three fundamental types, although there 

 are gradations between them. Other names are given to 

 certain species on account of the way in which the indi- 

 vidual cells may be joined to each other: i.e., if the cell is 

 isolated it is called a micrococcus; two coccus forms joined 

 closely are spoken of as diplococcus. Sometimes the cells 

 may adhere in long chains and are then known as strepto- 

 coccus. If they form clusters instead of chains they are 

 called staphylococcus. A few coccus forms grow out in a 

 platelike expansion, when they are called tetrads. If they 

 multiply in three directions of space instead of in two 

 they form cubical masses known as saroina. 



