2 Agricultural Bacteriology. 



Structure of bacteria. Plants and animals are made 

 up of cells which are tiny masses of semi-liquid matter 

 surrounded by a membrane, the cell wall. Many kinds 

 of cells are found in each individual higher plant 

 or animal. The sum total of the activities of all the 

 cells constitutes the life of the individual. Bacteria are 

 made of cells the same as other living things, but in- 

 stead of a number of cells being required to form an 

 individual, each cell is a complete organism in itself, 

 capable of carrying on all the processes necessary for 

 the continuance of its life. The single cell can breathe, 

 take in food, live, and reproduce itself. Thus while the 

 bacteria are very simple as to their structure, they per- 

 form all the necessary functions of a living organism. 



A B C ;. 



FIG. 1. FORMS OF BACTERIA. 

 A, coccus; B, bacillus; C, spirillum. (After Novy.) 



Forms of bacteria. Where the individual is reduced 

 to the limits of a single cell, it is evident that not much 

 variation in form is possible. While slight variations 

 in size and shape are to be noted, nearly all the bacteria 

 may be grouped under three general types. The ball- 

 shaped are known as cocci (singular coccus) ; the rod- 

 shaped are called bacilli (singular bacillus) ; if the rods 

 instead of being straight are more or less curved, they 

 are known as spirilla (singular spirillum). The ball- 

 shaped and the rod-shaped are by far the most abun- 

 dant and are the forms of most interest to the student of 

 agricultural bacteriology. 



