INTRODUCTION TO THE PROTOZOA 



23 



Histomonas meleagridis , the cause of 

 blackhead of turkeys, was discovered by 

 Theobald Smith in 1895. Its transmission 

 in the eggs of the cecal worm was discov- 

 ered by Tyzzer and Fabyan in 1922 and 

 described in detail by Tyzzer in 1934. 



The first parasitic amoeba, Enta- 

 moeba gbtgivalis, was found in the human 

 mouth by Gros in 1849. Lewis found E. 

 coli in India in 1870, and Losch found E. 

 histolytica in Russia in 1875. 



Balantidium coli was discovered by 

 Malmsten in 1857. 



It was not until 154 years after Leeu- 

 wenhoek saw Eimeria stiedae that any 

 other telosporasids were found. Then, in 

 1828, Dufour described gregarines in the 

 intestines of beetles, and in 1838 Hake 

 rediscovered the oocysts of E. stiedae. 

 The most extensive early study of the coc- 

 cidia was that of Eimer (1870), who des- 

 cribed a number of species in various 

 animals. Schaudinn and Siedlecki (1897) 

 described the gametocytes and gametes of 

 coccidia and showed that they formed 

 zygotes. Further studies on the life cycle 

 of coccidia were published by Schaudinn 

 in 1898 and 1899. Classic work on the 

 coccidia of gallinaceous birds was done by 

 Tyzzer (1929) and Tyzzer, Theiler and 

 Jones (1932). 



The human malaria parasite was dis- 

 covered in 1880 by the French army doctor, 

 Alphonse Laveran. Golgi (1886, 1889) re- 

 ported on its schizogony and distinguished 

 the types of fever caused by the different 

 species. MacCallum (1897), working with 

 the closely related Haemoproteiis of birds, 

 recognized that the exflagellation which 

 had been seen by Laveran was microgamete 



formation, and later observed fertilization 

 and zygote formation in Plasmodium fal- 

 ciparum. 



Ross worked out the life cycle of the 

 bird malaria parasite, Plasmodium re- 

 lictum {P. praecox), in India in 1898, 

 showing that it was transmitted by the 

 mosquito, Culex fatigans . Working inde- 

 pendently in Italy, Grassi and his collab- 

 orators (1898) almost immediately after- 

 ward found that human malaria is trans- 

 mitted by Anopheles mosquitoes. 



Babesia bovis was discovered by 

 Babes in 1888. Theobald Smith and Kil- 

 borne described the cause of Texas fever 

 of cattle, B. bigemina in 1893; they showed 

 that it was transmitted by the tick, Boo- 

 philus annulatus, being passed thru its 

 eggs to the next generation of ticks which 

 then infected new cattle. This was the 

 first demonstration of arthropod trans- 

 mission of a protozoon. 



The present century has seen many 

 advances in protozoology, but there are 

 many more ahead. Several times more 

 species of parasitic protozoa have been 

 described since 1900 than were known be- 

 fore, but these are only a fraction of the 

 total number. Exciting new discoveries 

 are being made every year on the physi- 

 ology and nutritional requirements of pro- 

 tozoa (Lwoff, 1951; Hutner and Lwoff, 

 1955), and the life cycles, host-parasite 

 relations, and pathogenesis of many spe- 

 cies are only now being worked out. The 

 electron microscope and the phase micro- 

 scope have opened up a whole new field 

 for morphologic study, chemotherapy is 

 progressing rapidly, and new discoveries 

 are being made even in taxonomy, which 

 most people used to consider a dead field. 



CLASSIFICATION 



Various classifications have been proposed for the Protozoa. They have been dis- 

 cussed by Hall (1953) and also by Biocca (1957). The classification used in the present 

 book is based on those used by Jahn and Jahn (1949) and Hall (1953), with certain mod- 

 ifications; the classification of the Ciliasida is based on Corliss (1956, 1959). The uni- 

 form endings for the names of higher taxa proposed by Levine (1959) are used. Most of 

 the groups not of veterinary or medical interest are omitted. In addition, some genera 



