22 



Insects and Disease 



The members of the class Infusoria, so called 

 because they were early found to be abundant in 

 various infusions, are characterized by numerous 

 fine cilia or hair-like organs by means of which the 

 organism moves about and procures its food. The 

 well-known " slipper animalcule' ' (Paramoecium) 

 (Fig. n), and the " bell-animalcule' ' (Vorticella) 

 (Fig. 12) are two common representatives. The 

 Paramoecia were the animals mostly used by Jen- 

 nings in his wonderfully interesting experiments 

 on the behavior of these lowly forms of life. He 

 showed that they always reacted in a certain defi- 

 nite way in response to particular stimuli, and he 

 was led to believe that he could see "what must 

 be considered the beginnings of intelligence and 

 of many other qualities found in the higher ani- 

 mals.' ' A species of Vorticella was probably the 

 first Protozoan that was ever observed. An old 

 Dutch microscopist, Anton von Leeuwenhoek, in 

 1675, while studying with lenses of his own manu- 

 facture, discovered and described forms which un- 

 doubtedly belong to this genus. Few if any of the 

 Infusoria are pathogenic, although some are said 

 to be associated with certain intestinal diseases 

 both in man and the lower animals (Fig. 13). 



The last class, the Sporozoa, or the spore-forming 

 animals, while small in the number of known spe- 



