March 21, 1901] 



NATURE 



At the present time, however, though our knowledge of 

 the HasmamoL'bidae has so much increased and though 

 their pathological significance is now more clearly de- 

 fined, yet we cannot say certainly that all the species 

 which invade man have been identified. 



In England we group all malaria parasites under three 

 heads : — 



(i) Haemamoeba malariae^ the parasite of Quartan 

 fever. 



(2) Haemamoeba vivax, that of Tertian fever. 



(3) Haetnamoeba precox, that of Quotidian or aestivo- 

 autumnal fever. 



But in Italy Grassi states positively that he has ob- 

 served a fourth species, which he names Haemamoeba 

 imtnaculaia. This species is without pigment and has 

 been accepted by Marchiafava and Bignami, but oyr 

 knowledge of the facts is still somewhat limited. In 

 West Africa the first expedition which went out to in- 

 vestigate malaria was inclined to divide H. vivax into 

 two distinct species differing in the colour of their pig- 

 ment, one with fine brown and the other with fine black 

 granules. Furthermore, it has been suggested that 

 H. precox may be also split into two or more distinct 

 species. 



On these points we must await the results of patiept 

 investigations now pending. 



For many years after the inseparable association of the 

 Haemamrebidas with malaria had been demonstrated, the 

 means whereby they could enter the blood and attack 

 the corpuscles was unknown. But at last the work of 

 Ross in India (with which Manson must ever be asso- 

 ciated) enabled us to see light. King (1841) had sus- 

 pected that mosquitoes were a factor in malarial infection, 

 as also had Laveran : but Ross led us, by his researches 

 in the life-history of H. relicta (the parasite of birds), 

 from mere hypothesis to fact. Confirmation was soon 

 forthcoming in Italy, a country where the prevention of 

 malaria is of great economic importance ; and later ex- 

 peditions were dispatched by the Liverpool School of 

 Tropical Medicine, the Royal Society and the German 

 Government to various malarial districts, to thresh out 

 the wholequestion and to evolve, if possible, some practical 

 method or methods of prophylaxis. 



Valuable experiments, too, were made in the Roman 

 Campagna last year by the London School of Tropical 

 Medicine, which afforded valuable confirmation of the 

 views advanced by previous expeditions. More recently, 

 too, an expedition from Liverpool has returned after 

 making a complete survey of the lower reaches of the 

 Niger, with the result that previous observations have 

 been confirmed and further additions to our knowledge 

 made. 



Now we know, with a certainty rarely attained in 

 medical matters, that malaria, instead of being inhaled 

 with the night air as a noxious miasm from marshy 

 countries or ingested with water, as was at one time 

 suggested, is caused by the direct injection of animal 

 parasites into the blood by mosquitoes previously infected 

 by some human being suffering from the fever. 



Careful microscopic work has shown that the Haema- 

 moebidae of human malaria are parasitic not only in man 

 but also in certain mosquitoes. 



The parasites have two phases in their cycle of 

 development, and need a different host for the com- 

 pletion of each phase, that is to say, that like many 

 other well-known parasitic organisms, they exhibit 

 " alternation of generation," in which man is the " inter- 

 mediary" and mosquito the "definitive" host. 



But it has been proved that all mosquitoes are not 

 hospitable to the hasmamcebidte of malaria. One genus 

 only — Anopheles — has so far been convicted, though 

 Culex has been subjected to an equally searching cross- 

 examination. 



Although Anopheles, as compared with Culex, is a 



NO. 1638. VOL. 63] 



small genus with a comparatively limited distribution^ 

 yet all its species have not been proved hospitable. 



In West Africa A. Costalis and A. funestus, in British 

 Central Africa A. funesius, in the West Indies A. 

 Costalis (?), in Italy A. Maculipentiis, are the species 

 chiefly concerned as agents of transmission. 



With the information at present obtainable it must, 

 therefore, not be too hastily concluded that the whole 

 genus Anopheles is hospitable to the parasites, but I 

 venture to say that it may now fairly be assumed, on the 

 other hand, that no species of Culex ever conveys the 

 human parasites, though this genus is chiefly concerned 

 as definitive host of the avian hasmamoebidas. 



White men who have travelled in the tropics say,, 

 assuming what you teach about the parasitic nature 

 of malaria and the part played by mosquitoes to be 

 the truth, there remains the question as to where the 

 mosquitoes originally became infected. This was for a 

 time a mystery, but the recent work of Koch in Java 

 and Stephens and Christophers in West Africa has 

 afforded an explanation. These observers independently 

 discovered that though adult natives suffered little or 

 nothing from malaria, yet their children from earliest 

 infancy exhibited great numbers of parasites in their 

 blood, though, like their parents, they rarely showed 

 marked symptoms of infection. The blood of 80 to- 

 90 per cent, of native children in some districts has been 

 shown to contain parasites, and it has been noticed that 

 these varied in number inversely as the number of years 

 of life ; that is to say, evidence of parasitic invasion 

 decreased as the children grew to manhood, and gradu- 

 ally a condition of partial immunity was attained. 



Similar instances of acquired immunity are occasion- 

 ally seen among white men who have lived many years 

 in malarious countries. The mechanism of this immunity 

 is as yet unknown. 



It appears, therefore, certain that the prime source of 

 mosquito infection is the native children, who, though 

 not indifferent to mosquito bites, appear to view their 

 ravages with equanimity. It follows, then, that the 

 proximity of native habitations is a constant menace to- 

 the health of white men provided that the necessary con- 

 necting link— Anopheles— is also present. In considering 

 the best means of prophylaxis, it will be seen that im- 

 portant deductions have been drawn from these facts. 



The prime cause of malaria being known, its method 

 of invasion having been satisfactorily demonstrated and 

 the official seal of scientific approval to these facts having 

 been obtained in Lord Lister's recent address to the 

 Royal Society, it remains now to apply our knowledge 

 in a practical way, so as to evolve some method or 

 methods of prophylaxis and thereby crown a piece of 

 scientific work as far reaching in its power to benefit the 

 whole human race as any of those brilliant discoveries 

 which have made the Victorian age conspicuous above 

 all others. 



And that this is not the language of exaggeration is 

 readily seen when one considers the enormous tale of 

 deaths caused annually throughout the world by malaria, 

 and when one realises how much the control and develop- 

 ment of new territory are arrested by the constant 

 invalidism of Government officials, medical officers and 

 traders in tropical climates, where it is constantly neces- 

 sary to employ two men to do the work of one. 



This latter point will appeal specially to those who- 

 recognise that the British Empire is now world-wide 

 and tending to still further extend its borders. 



During the last two years various authorities o» 

 paludism abroad, and members of the various expeditions 

 from England, have made suggestions and recommen- 

 dations as to the prophylactic measures which should be 

 taken in consequence of the recent additions to our 

 knowledge. . 



Some have advocated wholesale destruction of 



