86 THE ANIMAL PARASITES OF MAN 



parasites in birds, investigators directed their attention to the study of the 

 haemosporidia of birds, Grassi and Feletti (n), Celli and Sanfelice (12), Kruse 

 (13), Labbe (14). The last-mentioned author also demonstrated the existence 

 of analogous forms in reptiles and amphibious animals in a masterly way. 



Several authors gained great credit in collecting and compiling the 

 scattered and fragmentary knowledge contained in a great quantity of litera- 

 ture. Amongst the works of these authors (15), Mannaberg's (16), which 

 includes his independent personal researches, is highly commendable, as is 

 also Ziemann's book (17). These works should be consulted for the literature 

 not mentioned here. 



The conclusions arrived at, however, still left many important questions 

 unanswered. Nobody was in a position to state with any certainty in 

 what manner the infection of man (apart from that of animals) was 

 brought about, nor were there any well-grounded demonstrations of how 

 the cause of malaria, according to analogy with other parasites, left the 

 body of the host, nor what was its subsequent fate. Neither of the 

 theories advanced explain the matter ; for even conceding the existence of 

 malarial germs in the air and their invasion of the human body by way 

 of the air passages, it remained an enigma why the germs should only 

 occur at a slight elevation above the soil, or should only exist in certain 

 compartments of many houses, or why they were not distributed in all 

 directions by currents of air, &c., &c. 



The last few y ears have thrown light on this subject. Several investi- 

 gators, working almost simultaneously and partly quite independently, have 

 come to the conclusion that blood-sucking animals play a part in malaria. 

 For certain reasons a few blood-suckers could be rejected at once, others, 

 such as mosquitoes, appeared to be particularly suspicious. 1 Manson (18) was 

 the first to call attention to the mosquito, knowing from his own experience 

 the part played by these insects in the further development of the filariae 

 of the blood of man. Here, as in malaria, the mosquitoes are. supposed to 

 suck up the parasites with the blood of human beings and to void them 

 ultimately into the water, so that hereby there is at least the possibility of 

 infection of other hosts. Bignami (19) was of an exactly opposite opinion 

 as to the vole of the mosquito, which had been, in Italy, brought into connec- 

 tion with malaria ages since, a belief which, according to Koch (20), was also 

 shared by the natives of Africa. Supported by the experimental inoculations 

 first undertaken and subsequently repeated by Gerhardt, Bignami gave it 

 as his opinion that mosquitoes having themselves become infected by a still 

 unknown stage of malarial parasites occurring in the open, inoculated them 

 into man with their bite. This opinion, which was supported by the part 

 played by ticks (Boophilus bovis} living on cattle in the transmission of 

 the agent of Texas fever (Piroplasma bigeminum}, seemed to explain many 

 obscure points, but the experiments conducted by Bignami and Dionisi to 

 substantiate this view gave negative results. 



R. Koch (20) combined the respective theories of Manson and Bignami, 



1 Nuttall, G. H. F., " Die Mosquito-Malariatheorie " (C. /. B., P. u. I., 1899, xxv , 

 pp. 161, 209, 245, 285, and 337). 



2 The correct name of this Tick is Rhipocephalus annulatus (Say). The disease is 

 called Redwater in Africa, and is known by this name in other places. In Africa the 

 carrier is R. decoloratus (Koch), in Germany Ixodes reduvius acts as carrier. (F.V.T.). 



