November 5, 1914] 



NATURE 



269 



It is found almost ever}-where in hot climates, and 

 even in most temperate climates during the summer. 

 From statistics we find that as a broad general rule 

 in malarious countries about one-third of the total 

 population suffers from attacks ever\' year, and also 

 that about one-third of the admissions to hospital and 

 attendances at dispensaries are due to malaria. But 

 these figures are merely based upon records, and do 

 not cover the enormous additional number of patients 

 who remain untreated. Thus we know that the 

 malaria-parasites or malarial enlargement of the 

 spleen can be found in native children in malarious 

 countries to an enormous extent, reaching loo per 

 cent, in ven.- insalubrious spots. The case mortality 

 is only about 05 per cent., but the prevalence of the 

 disease is so extremely great that the total mortalitv 

 caused by it makes an addition to the general mor- 

 tality of anything up to 10 per mille, or even 15 per 

 mille; and the malady complicates all other diseases 

 in the tropics in a way which renders them more 

 difficult to treat. In India alone it has been officially 

 estimated that the total deaths from malaria average 

 about 1,300,000 a year in ordinary- years, and mav 

 reach a much higher figure during years of epidemic 

 prevalence. Thus the total bill of annual mortality 

 and sickness which King Malaria presents to the 

 human race is something enormous. 



Hence the development of the human race, especiallv 

 in warm countries, has long demanded that we should 

 ascertain exactly how this plague is propagated and 

 should endeavour to find how best it may be prevented. 

 It is remarkable that even more than five hundred 

 years before Christ the ancients certainly were 

 acquainted with one great law, namely, that malaria 

 is connected with stagnant water, such as marshes ; 

 and there are good grounds for believing that Empe- 

 dokles of Sicily actually delivered Selimis from malaria 

 by draining its marshes or by turning two rivers into 

 them. This knowledge seems to have been generally 

 held since ancient times, though it must have been 

 acquired quite empirically; but Varro and Columella, 

 at about the time of the Christian era, actually sug- 

 gested that the disease is in some way connected with 

 insects which breed in marshes. In more modern 

 times, however, malaria has been ascribed to noxious 

 vapours given off by stagnant collections of water— 

 the hypothesis evidently being that the poison is some 

 kind of chemical one. I have mentioned that in 1880 

 Laveran discovered that the disease is due to certain 

 protozoal parasites in the blood. When thi^ fact was 

 accepted ten years later, many observers at once 

 rushed to the conclusion that these parasites have an 

 extra corporeal existence in marsh water, and actually 

 attempted to demonstrate this by producing infection 

 in healthy persons by such water brought from mala- 

 rious localities. The experiments of Agenore Zeri 

 (1890) are to be particularly mentioned. He gave 

 water from the Pontine marshes persistently to a 

 number of persons oraUy or in spray, or by clyster — 

 but entirely without result. At the same time many 

 thought that the poison may lie, not only in stagnant 

 water, but generally in the soil of warm countries — 

 this being called the hypothesis of the telluric miasma ; 

 but, of course, this was merely a hypothesis which 

 did not rest upon any obser\'ations or experiments. 

 Even ten years after Laveran 's discovery we were still 

 completely ignorant as to how the malaria parasites 

 enter the body. We might search for them in marshes 

 and soil ; but the search was likely to prove extremely 

 difficult, because all water and soil is full of innumer- 

 able different organisms, and it would have been no 

 light task to ascertain which of all these are really 

 responsible for the disease among men, especially since 

 Zeri had shown how difficult it was to produce infec- 

 tion bv means of water in bulk. 



NO. 2349, yoL. 94] 



\ At the same time, however, the hypothesis origin- 

 ally but vaguely mooted by \'arro and Columella had 

 ; been gaining ground. Indeed, Lancisi had repeated 

 i the same speculation in 1717, and seems actually to 

 ' have suspected mosquitoes and to have studied them. 

 I So late as i88i several theorists repeated this concep- 

 : tion, though on studying their statements I think 

 ; that little value is to be attached to them. In 1883, 

 I however, Dr. A. F. -A. King wrote a most able paper 

 i on the subject, in which he gives no fewer than nine- 

 1 teen reasons why mosquitoes are likely to carr>' 

 ' malaria. He thought that the insects bring the poison 

 I from the marsh and inoculate it into men. Many of 

 ' his reasons are good, but others are now seen to 

 ; have been untenable — and, in any case, he gave no 

 experimental evidence. Next year, Laveran himself 

 ' and Robert Koch independently enunciated the same 

 ; speculation, but gave few reasons and no experiments 

 in support of it. Ten years later, however, Manson 

 ; repeated the hypothesis, but in a different form. He 

 ' depended less upon the epidemiological evidence cited 

 I by King than upon certain parasitological evidence 

 J which occurred to himself. By this time (189J) the 

 I parasites of malaria had been very carefully studied, 

 j and were shown to possess, not only certain forms which 

 , provide for their propagation in the human host, 

 i but also other forms which, when the blood is freshly 

 1 drawn, emit several so-called flagellated bodies. These 

 latter forms had really led Laveran to his discover^', 

 but their zoological significance still remained quite 

 unexplained, and while some writers thought that thev 

 ! had some special significance, others believed them to 

 I be merely the result of death in vitro. Manson now 

 i urged that the flagellated bodies given off from these 

 ! forms are really flagellated spores ; that when mos- 

 ! quitoes ingest blood containing these forms, the 

 j flagellated spores escape in the insect and enter its 

 tissues, where they ripen into some further unknown 

 stage. Then, he thought, the insect dies two or three 

 days later on the surface of the water, and this later 

 stage of the parasites enters the water, and finally 

 rises in the marsh mist to infect man. Obviously 

 therefore Manson 's h\f)othesis was quite different from 

 King's; the former thought that mosquitoes derived 

 the parasite from men and transferred it to the marsh, 

 while King though just the opposite. Neither really 

 reached the wonderful truth : both were half right, 

 both half wrong. One cited parasitoWgical and the 

 other epidemiological evidence; and neither attempted 

 experimental verifications. 



Nevertheless, all these hypotheses, including those of 

 the telluric miasma, were necessar}- for the laborious 

 experimental inquin,- which was now evidently de- 

 manded in the supreme interests of human life and 

 health. I gather from what 1 have been told that 

 my own work on the subject may prove sufficiently 

 interesting to students to be worthy of mention here. 

 I was first drawn to the malaria problem in the year 

 1889, when I obser\ed during active ser\-ice in Burma 

 that the prevalence of malaria did not at all accord 

 with the theon.- of the telluric and marsh miasma ; 

 and my doubts were strengthened during subsequent 

 years by careful thought and study. If the poison is 

 given off in an aerial form either from water or from 

 soil, the disease ought to be almost uniformly dis- 

 tributed. Such, however, is not the case, and it really 

 occurs principally in ven.' small spots or pockets, 

 generally in close proximitv" to stagnant water. Thus 

 in one station where I afterwards ser\ed, my regiment 

 was severely inflicted, while other regiments, scarcely 

 a mile distant, remained almost entirely free. I was 

 therefore verj- dissatisfied with this hypothesis, and 

 being acutely alive to the great importance of the 

 problem, I determined to study it carefully. In 1894 

 Manson acquainted me with his hypothesis, and I then 



