2 INTRODUCTION 



with in considerable numbers, and frequently several 

 kinds are visible. These all belong to the Animal King- 

 dom, and are included in the Protozoa, a division which 

 embraces the simplest forms of animal life. 



Small pieces of leaves may also be observed in most 

 instances, as well as other bits of dead material. In 

 addition to these there will always be visible hundreds 

 of exceedingly small rod-shaped bodies distributed about 

 in the water. They are so minute, however, that unless 

 the attention is specially directed to them they may 

 easily be overlooked. By careful observation they are 

 seen to be of variable lengths and capable of independent 

 movement, travelling end on backwards and forwards 

 through the liquid. 



Fig. 2 is a more highly magnified view of a portion of 

 a drop of a hay infusion, an J-inch objective being used 

 in this case. The large oval body, d, is one of the 

 Protozoa referred to above ; b is a piece of mould fungus, 

 and some of its spores or reproductive bodies are seen at 

 c. They are non-motile. The living, rod-like organisms 

 are now easily seen, and their movements more readily 

 followed. Some of the longer ones are depicted in the 

 figure at d, and others of a different form and size are 

 shown at e. 



2. These minute living things are examples of 

 organisms known as bacteria. They are distributed all 

 over the world in incalculable numbers in the air, in 

 water, in the soil, and wherever dust can be carried. 

 Their importance can scarcely be over-estimated, as they 

 are responsible for some of the most striking phenomena 

 in nature. They carry on useful work in preparing the 

 soil for the growth of crops, and render manures which 

 are applied to the land efficient for the nutrition of 



