Though P. falciparum is the most malignant and spreads most rapidly when anophelism is intense, because of its greater output of gametes in the blood, it does not tend to such chronicity in the absence of reinfection as do the other two forms. In the absence of reinfection P. malariae, by far the rarest form, is, however, the most resistant and P. vivax holds an intermediate place. Of 28,270 blood examinations made in England at one laboratory on cases of malaria contracted during the World War, 777 were found positive, and of these P. vivax numbered 759, P. falciparum 14, P. malariae four. There was a marked tailing off as the time in England lengthened, and it was rare to find the parasite of ter the quarterly period of 12 to 15 months. Seven cases were found after 3o months all with P. vivax, one in a double infection with P. malariae of ter 39 months, and one case after 51, and another after 59 months ; P. falciparum was found after three months in a double infection with P. vivax at the 1 i th month, once alone at the 12th month, and once in a triple infection at the 14th month. The third of the four cases of P. rnalariae had also been home a lung time, namely, 16 months. In none of this ex tensive series was the parasite ever found after five years at home. It is not uncommon to hear a person settled in a non inf ective country for many years accusing a temporary febrile attack or period of lassitude as a return of malaria which he once contracted abroad. Proof of this seems wanting. Though malaria has been transferred directly from man to man, the parasites infecting man have not been made to infect any animal. Ento mologists have furthered their investigations into the bionomics and classification of mosquitoes and the determination of the species of anopheles that carry malarial parasites.
S. P. James and Dale have reported that quinine, quinidine and cinchonine possess the same curative properties for all forms of malaria, and without difference in their toxicity save for the greater cardiac depressant action of quinidine. Fletcher at Kuala Lumpur has made a careful series of observations on this point.
Many clinicians strongly advocate in tropical regions intra muscular and intravenous injections of the bihydrochloride of quinine in serious cases, and injections do act quickly in severe, malignant, remittent and comatose cases, but in ordinary cases oral administration of the sulphate has been satisfactory. In acute attacks it must be borne in mind that 24 hours or more may elapse before the good effects of quinine become manifest.
The classical successes in the reduction of malaria at Ismailia, Hongkong, Havana and elsewhere have encouraged similar work in other localities, but there are few such examples as the long continued labours of M. Watson in the Federated Malay States
and the brilliant sanitary victory of Gen. Gorgas and the Ameri cans over both malaria and yellow fever at Panama. The work of Darling, Bass and others in southern United States and in the islands must also be mentioned. The method of mosquito re duction against malaria, first suggested and tried under Ross in Freetown, Sierra Leone, in 1899, has not been followed as widely as anticipated, and local authorities too often dislike spending money on sanitation and hamper practical efforts of sanitarians by the attitude that it is better to prevent malaria by quinine or by the use of mosquito-nets, measures impractical in an un educated native community. Local conditions must always de termine the most suitable mode of prophylaxis, and it is im portant, as E. Sergent points out, to have several methods of control which may well be combined and include with specific measures an educational propaganda. Obviously there must be action to eliminate infection from all carriers of the parasite; in other words, to prevent the mosquito becoming infected, to destroy the species of Anopheles in which the parasite may de velop, and to prevent their biting and inoculating the parasite into the blood of man. Good results have attended well-applied efforts of this kind. Better health results and there are real eco nomic returns for expenditure. The native must be looked after and enjoined to adopt some sanitary methods until he is taught to share in systematized efforts to protect and cure himself of malaria as of other endemic diseases.
Measures to rid carriers of the parasite are most difficult to put into practice. There is no settled or fixed dosage, or time of administration, of the specific remedy, quinine or other of the cinchona bark extracts. Acute attacks respond readily to quinine; each dose makes a reduction in the number of parasites, and this reduction occurs every day, until finally none of the parasites is left. Treatment must be continued for a long time. Empirically three months appear to be enough, but there are obstinate cases.