2 Dairy Bacteriology. 



Structure Of bacteria. So far as structure is concerned 

 the bacteria stand on the lowest plane of vegetable life. 

 The single individual is composed of but, a single cell, the 

 structure of which does not differ essentially from that of 

 many of the higher types of plant life. It is composed of 

 a protoplasmic body which is surrounded by a thin mem- 

 brane that separates it from neighboring cells that are 

 alike in form and size. 



Form and size. When a plant is composed of a single 

 cell but little difference in form is to be expected. While 

 there are intermediate stages that grade insensibly into 

 each other, the bacteria may be grouped into three main 



r * i 



Fio. 1. Different forms of bacteria, a, b, c, represent different types as to 

 form: a, coccus, *, bacillus, c, spirillum; </, diplococcus or twin coccus ;<?, staphy- 

 lococcus or cluster coccus; / anl #, different forms of bacilli, g shows internal 

 endospores within cell; h and /, bacilli with motile organs (cilia). 



types, so far as form is concerned. These are spherical, 

 elongated, and spiral, and to these different types are given 

 the names, respectively, coccus, bacillus and spirillum 

 (plural, cocci, bacilli, spirilla) (fig. 1). A ball, a short 

 rod, and a corkscrew serve as convenient models to illus- 

 trate these different forms. 



In size, the bacteria are the smallest organisms that are 

 known to exist. Relatively there is considerable difference in 



