II32 



THE MALARIAL FEVERS 



/ 



With regard to this point the tendency at present is to beUeve that Schau- 

 dinn's observations will not be confirmed. 



3. Whether any mosquito other than the Anophelinae carry the parasites. 

 So far, no evidence in favour of this has been brought forward. 



4. Whether there is any animal other than man in which the parasites live 

 Jn nature. 



The investigations of Fermi and Lumbau in 191 2 are steps in answering 

 this question negatively, but many more observations in different countries 

 are necessary before a final answer can be given. Mesnil has succeeded in 

 infecting an orang-utan with simple tertian malaria. The attacks of fever 

 in this animal were mild, but for several weeks typical parasites were found. 



5. Whether there are any malarial parasites of man which have so far not 

 been recognized. 



Thus Stephens has insisted upon Plasmodium tenue, which does not appear 

 to us to be specifically distinct, and Oswaldo Cruz has invited attention to a 

 peculiar quartan type of parasite found in the valley of the Amazon and 

 associated with oedema of the legs as a pronounced symptom. Laloir's parasite 

 is mentioned in the next chapter, and several other observers have described 

 new varieties of the malarial parasites which require confirmation. 



6. Usually it is believed that all fevers regularly recurring every third or 

 fourth day are malarial, but this, while correct as a general rule, is open to 

 doubt in certain instances, and in any case requires careful watch. 



.ffitiology. — The setiology may be divided into: — 



I. The Exciting Causes. 

 II. The Predisposing Causes (p. 1142). 



I. Exciting Causes. — Malarial fevers are produced by the ^^dci^.- 

 sitesPlasmodium malaricB Laveran, i88i,P. vivax Grassi andFeletti, 

 1890, and Laverania malarice Grassi and Feletti, 1890, because they 

 are always found in the blood or organs of persons suffering from 

 the disease, and can be injected into healthy persons, producing 

 in them typical fevers, the different stages of which correspond to 

 the stages of the life-cycle of the parasite. .These parasites can be 

 spread from human being to human being by mosquitoes, in whose 

 bodies they undergo development as already described. Infected 

 mosquitoes can conve}' the parasites to healthy persons, living in 

 either non-malarial or malarial climates, by their bites, producing 

 attacks of fever typical for the type of parasite with which the 

 mosquito was infected. The classical experiment is the infection 

 of Sir Patrick Hanson's son with tertian malaria by means of infected 

 anophelines sent from Rome to London. 



There are, therefore, three factors necessary for the production 

 of malarial fever: (i) the blood parasite; (2) the mosquito; (3) man. 



I. The Blood Parasite. — We have drawn attention to three para- 

 sites in connection with malaria, and we believe these to be the only 

 three at present known to cause the fevers, but it is necessary to say 

 that this view is by no means universal. Some authorities believe 

 in a quotidian form of fever due to a species of Laverania, or to two 

 separate species of the same genus. These parasites, however, if 

 they exist as distinct species, which we believe to be very doubtful, 

 have not come within our observation, and we therefore agree with 

 those writers who only acknowledge the three types mentioned above. 



The descriptions of the structure and life-histories of these para- 



