196 POPULAR SCIENCE MONTHLY. 



the blood of malaria patients by Professor Danilewsky, in 1891. This 

 form differed from the ordinary parasites in having many fine, flagelli- 

 form appendages, which, breaking away from the parent, would swim 

 about freely in the surrounding fluid (Fig. 3, p). Danilewsky regarded 

 this form as an independent blood parasite, and gave to it the name 

 Polymitus. In a sense, Polymitus has been the key to the life history 

 of the malaria organism, and its history has been the history of the 

 further discoveries upon malaria. In France, Laveran regarded Dan- 

 ilewsky's discovery as indicating some stage in the cycle of Plasmodium 

 malarice, and not as an independent organism, while Labbe considered 

 Polymitus a degenerate condition of the ordinary parasites and without 

 further significance. The English specialist on tropical diseases. Dr. 

 Manson, found that the malaria parasites, when exposed with the 

 blood to the cooler air, very soon assume the Polymihis form, which 

 he regarded as the extra-corporeal form assumed by the malaria-' 

 organism, for, he argued, the wide distribution of malaria, the spread 

 from individual to individual, can be explained, since the disease is not 

 contagious, only by the assumption of germs outside of the body. Fur- 

 thermore, he suggested that these germs might be carried from person 

 to person, by insects, such as the mosquito. In the same year, Laveran 

 made an identical suggestion quite independently of Manson. It was 

 not altogether novel, however, with either of these investigators; thus 

 a certain mosquito in central Africa is known to the natives as the 

 fever organism, while the same idea was represented in Theobald 

 Smith's discovery (1893) of the tick as the agent in the transmission of 

 the 'Texas fever' of cattle. 



The first positive results on the significance of the Polymitus form 

 were obtained by MacCallum, in Washington, in 189T-'98. A similar 

 Polymitus form is developed by the malaria-organism of birds (Halter- 

 idium), and, in the blood of diseased crows, MacCallum observed the 

 filamentous motile bodies of the Polymitus form, break away from the 

 central mass, and unite with an ordinary parasite. The result of the 

 conjugation was a copula Avith an independent motion, by which it 

 made its way through the surrounding fluids. The later history of 

 the copula was not followed; similar observations were made, by the 

 same observer, upon living malaria-organisms of man, and the Polymitus 

 'flagella' were seen to unite with larger forms of the parasite. 



In the meantime, Major Ross, in India, was working out the mos- 

 quito hypothesis of Manson and Laveran, and succeeded in placing 

 that theory upon a very substantial basis. He found black pigment 

 granules, in the intestine and epithelial cells of the mosquito, which 

 were identified as melanin granules of the blood parasite. It was also 

 found, by Eoss, that only certain kinds of mosquitoes were selected 

 by the inalaria parasites, viz.: various species of the genus Anopheles 



