Bacteria and Protozoa 



21 



this class is the little green Euglena (Fig. 9), whose 

 presence in standing ponds and puddles often im- 

 parts a greenish color to the water. Then in the 

 salt water near the surface there are often myri- 

 ads of minute Noctiluca whose wonderfully phos- 

 phorescent little bodies glow like coals of fire when 

 the water is disturbed at night. Although this class 

 contains fewer forms than the preceding some of 

 these have within recent years been found to be of 

 great importance because they live as parasites on 

 man and other animals. The trypanosome whose 

 presence in the blood and tissues of the patient 

 causes that dreadful disease which ends in sleeping 

 sickness belongs here as well as do several other 

 similar kinds that produce serious troubles for va- 

 rious mammals and birds. The Spirochaeta, about 

 which there has been so much recent discussion, 

 also belong here. These are simple spiral-like 

 forms (Fig. 10), that are sometimes classed with 

 the simple plants, bacteria, but Nuttall and others 

 have shown very definitely that they should be 

 classed with the simplest animals, the Protozoans. 

 These are the cause of relapsing fevers in man 

 and of several diseases of domestic animals. It is 

 believed by certain eminent zoologists that when 

 the germ that causes yellow fever is discovered it 

 will be found to belong to this group. 



