Paul-Louis Simond and Coccidia.

In 1880, during a sojourn at Constantine, Alphonse LAVERAN discovered the e tiological agent of human malaria. During his microscopic observations of t he parasite in freshly collected blood LAVERAN'S attention was attracted to the movement of flagellar bodies in the preparations. For LAVERAN, these f lagellar bodies corresponded to living organisms, in fact he considered the m the most characteristic stage of the parasite; perhaps the sexual form of the parasite. In 1884, back in Paris at the military hospital VAL DE GRACE , A. LAVERAN showed these flagellated bodies to PASTEUR, ROUX and CHAMBERLA ND who all thought that is was impossible not to recognize a living body in this mass of protoplasm displacing the surrounding red blood cells with it s protruding flagella. As early as 1890, Elie METCHNIKOFF established a link between the flagellar bodies of LAVERAN and the stealthy stage of parasitic Coccidia infecting t he intestinal epithelium of salamanders it was the Pasteuriens and a few ot hers scientists like DANILEWSKI and PFEIFFER who firmly believed that the f lagellar forms were indeed a normal stage during the hematozoan life cycle. On the contrary GRASSI and the Italian school as well as the French protoz oologist LABBE were convinced that the flagellar bodies corresponded to a d egenerative form of the parasite provoked by the exposure of the parasites to air during slide preparation. In early 1896, P-L SIMOND joined METCHNIKOFF'S laboratory and was assigned to study salamander coccidia in order to clarify the nature of the flagella r bodies. in a very short period of time, SIMOND clearly demonstrated that the coccidia had two types of life cycles. one of which resulted in the for mation of flagellar bodies. SIMOND called the flagellar bodies "chromatozoi tes" due to the important quantities of chromatin twisted around the flagel lum. From these observations and the sperm-like movement bf the chromatozoites, SIMOND put forth the hypothesis that the chromatozoites were the male sexua l forms of the parasite. He noted that they were found in ail species of co ccidia, as well as in the different species of malaria causing hematozoans of man and birds. SIMOND went even further in his interpretation to suggest that malaria parasites undergo sexual reproduction. This was indeed true, but SIMOND thought erroneously that sexual reproduction in hematozoans woul d result in the formation of resistant spores like in the Coccidia. The sex ual reproduction hypothesis of malaria parasites was also formulated indepe ndently a year later by W. G. MACCALLUM (1898) working in the United States on Halteridium, a hematozoan infecting crows. Initially MACCALLUM was not aware of SIMOND'S work, but later gave SIMOND full credit for his work on C occidia. Furthermore, MACCALLUM observed the first lime the chromatozoite ( microgamete) enter a female element (macrogamete) to form a mobile worm-lik e stage of the parasite know today as the ookinete. In his writings SIMOND is very modest, giving most of-the credit to his men tors METCHNIKOFF and LAVERAN, but LAVERAN in an article which appeared in 1 899 recognizes P.-L. SIMOND as the first person having put forth the hypoth esis that the flagellar bodies of hematozoans causing human and bird malari a were the male forms of the parasite destined to fertilize the female elem ents.