PARASITIC PROTOZOA 357 



is one of the most dreaded of these. It is caused by S. dutioni, 

 and is transmitted by the bite of a common African tick, 

 Ornithodorus moubata, which has habits similar to those of the 

 bedbug. The relapsing, or remittent fever of Europe is caused 

 by S. recurrentis, and is probably transmitted by some blood- 

 sucking insect, possibly by the bedbugs. The relapsing fever 

 of America is caused by 5". novyi. The mode of infection is not 

 definitely known. Yaws, a disease of the tropics which is 

 characterized by numerous ulcerating sores on the body, is 

 caused by Spirochata pallidula. It is thought that the common 

 house-fly plays an important part in its dissemination. Of the 

 diseases of domestic animals caused by spirochsetes a fatal 

 disease of fowls known as spirochaetosis is the most important, 

 as it may kill all the fowls in the chicken yard in the course of a 

 few days. It is caused by Spirochada marchouxi (gallinarum) 

 and is transmitted by ticks, usually by the common chicken 

 tick, Argas persicus. 



Syphilis. To the genus Treponema belongs a single im- 

 portant parasite, T. pallidum, that used to be classed with the 

 Spirochceta. It is the cause of that terrible disease, syphilis, 

 which results in untold suffering not only among those individ- 

 uals who are responsible for its dissemination but among many 

 innocent persons as well. Much of the syphilitic disease that 

 is in the world to-day is due to the infection of infants before 

 or at the time of their birth. 



MALARIAL FEVERS AND OTHER DISEASES CAUSED BY SPOROZOA 



The Sporozoa,or spore-forming Protozoa, include the smallest 

 but by no means least important members of the branch. 

 They are all parasitic and vary greatly in appearance, organiza- 

 tion and life history. They are so very plastic that they can 

 adapt themselves readily to their various hosts. Some of 

 them live during some stages of their development in the blood 

 cells of man and other vertebrates, the rest of their life being 

 passed in insects or other invertebrates. Malarial fevers are 

 caused by such parasites. Those that occur in man belong to 

 the genus Plasmodium. The three most important species are 



