THE PROTOZOA 229 



soon follows infection, and later general debility sets in. The 

 victim exhibits an increasing tendency to sleep, gradually wastes 

 away, and finally dies. 



Yellow Fever. — As stated in Chapter IX (p. 86) we do 

 not know what is the cause of yellow fever, but it is doubt- 

 less a germ of some kind, probably similar to the malarial fever 

 parasite. 



Spirochetes. — Spirochetes are corkscrew-shaped organ- 

 isms about 2tW °f an mcn l° n g (Fig- 136, C). They are usually 

 considered Protozoa, but their exact nature is not certainly 

 known. Many of the most terrible of all diseases are caused by 

 these minute living things. 



Yaws is a disease of the tropics characterized by the presence 

 of ulcerating sores on various parts of the body. It is caused 

 by Spirochceta pallidula. 



Syphilis likewise causes ulcerating sores. The organism re- 

 sponsible for this disease has been known for only a few years. 

 It is Spirochceta pallida. Recently a drug known as dichlorhy- 

 drate-diamido-arseno-benzol has been discovered which seems 

 to be an absolute cure for the disease. 



Relapsing or Recurrent Fever (see p. 101) occurs in some 

 parts of Europe. Another spirochsete, Spirochceta obermeieri, 

 is the organism that causes it. 



Kala Azar or Dumdum Fever (see p. 100) is a chronic dis- 

 ease in many parts of Asia and about the Mediterranean Sea. 

 It is characterized by irregular fever, an enlarged spleen, and 

 emaciation. The parasite that causes it is known as Leish- 

 mania donovani. 



Control of Pathogenic Protozoa. — All of the diseases caused 

 by pathogenic Protozoa are difficult to cure, and it is therefore 

 important that their infectious nature be understood by every 

 one, so that healthy people will not carelessly expose them- 

 selves and that diseased individuals will be careful not to dis- 

 tribute the parasites. Many of the protozoan parasites are 

 transmitted by insects or mites and ticks, and methods of con- 



