INTRODUCTION 15 



observed the microgamete formation in Haemoproteus of birds and 

 suggested that the "flagella" observed by Laveran were micro- 

 gametes of Plasmodium. In fact, he later observed the formation of 

 the zygote through fusion of a microgamete and a macrogamete of 

 Plasmodium falciparum. Almost at the same time, Schaudinn and 

 Siedlecki (1897) showed that anisogamy results in the production of 

 zygotes in Coccidia. The latter author published later further ob- 

 servations on the life-cycle of Coccidia (1898, 1899). 



Ross (1898, 1898a) revealed the development of Plasmodium 

 r dictum (P. praecox) in Culex fatigans and established the fact that 

 the host birds become infected by this protozoan through the bites 

 of the infected mosquitoes. Since that time, investigators too numer- 

 ous to mention here (p. 600), studied the biology and development 

 of the malarial organisms. Among the more recent findings is the 

 exo-erythrocytic development, fuller information on which is now 

 being sought. In 1902, Dutton found that the sleeping sickness in 

 equatorial Africa was caused by an infection by Trypanosoma gam- 

 biense. In 1903, Leishman and Donovan discovered simultaneously 

 Leishmania donovani, the causative organism of "kala-azar" in 

 India. 



Artificial cultivation of bacteria had contributed toward a very 

 rapid advancement in bacteriology, and it was natural, as the num- 

 ber of known parasitic Protozoa rapidly increased, that attempts to 

 cultivate them in vitro should be made. Musgrave and Clegg (1904) 

 cultivated, on bouillon-agar, small free-living amoebae from old 

 faecal matter. In 1905 Novy and MacNeal cultivated successfully the 

 trypanosome of birds in blood-agar medium, which remained free 

 from bacterial contamination and in which the organisms underwent 

 multiplication. Almost all species of Trypanosoma and Leishmania 

 have since been cultivated in a similar manner. This serves for de- 

 tection of a mild infection and also identification of the species in- 

 volved. It was found, further, that the changes which these organ- 

 isms underwent in the culture media were imitative of those that 

 took place in the invertebrate host, thus contributing toward the 

 life-cycle studies of them. 



During and since World War I, it became known that numer- 

 ous intestinal Protozoa of man are widely present throughout the 

 tropical, subtropical and temperate zones. Taxonomic, morphologi- 

 cal and developmental studies on these forms have therefore ap- 

 peared in an enormous number. Cutler (1918) seems to have suc- 

 ceeded in cultivating Entamoeba histolytica, though his experiment 

 was not repeated by others. Barret and Yarborough (1921) culti- 



