52: 



NATURE 



[March 29, 1900 



mische Nachrichten (Bd. 152, No. 3629) an extension of the 

 method put forward by Lehmann-Fildes {Astr. Nacli. No. 3242) 

 for the determination of the orbit of a spectroscopic double from 

 the observation of the velocities in the line of sight. The chief 

 characteristic of the present method is that the solution by 

 mechanical quadratures formerly necessary is here dispensed 

 with, thus somewhat simplifying the problem. 



MALARIA AND MOSilUITOES.^ 



OUR knowledge of the disease called malarial fever first 

 emerges from chaos in the seventeenth century, when, 

 owing to the recent discovery of quinine, the great Italian 

 physician, Torti, was able to differentiate this malady from other 

 fevers, and to describe its symptoms with accuracy. Next cen- 

 tury Morton, Lancisi, Pringle and others observed the connec- 

 tion of the disease with stagnant water and low-lying ground, 

 and first emitted the theory— which in one form or another has 

 found general acceptance up to the present date — that the fever 

 is due to a miasm which rises from the soil or water of malarious 

 localities. The next great advance was made in the middle of 

 the nineteenth century by Meckel, Virchow and Frerichs, who 

 ascertained that the distinguishing pathological product of the 

 disease is a black substance, which is distributed in collections 

 of minute coal-black or brown granules in the blood and organs 

 of patients, and which is called the tnalarial pigment or 

 melanin. This line of research culminated in the great dis- 

 covery of Laveran in 1880 — to the effect that the melanin is pro- 

 duced within the bodies of vast numbers of minute parasites 

 which live in the red blood-corpuscles of the patient. 



Ray Lankester had already opened the science of the parasit- 

 ology of the blood by his discovery of Drepanidiuni raitarum 

 in frogs ; and it was at once apparent that the parasites found 

 by these two observers are somewhat nearly allied — that is, that 

 Laveran's parasite is a Protozoal organism, and not a vegetable 

 one like the pathogenetic organisms recently discovered by 

 Pasteur, Lister, Koch and many others. And our knowledge 

 of the subject was quickly increased by the discovery of similar 

 haematozoa in certain species of reptiles, birds, monkeys and 

 bats, and in cattle, by Danilewsky, Kruse, Labbe, Koch, 

 Dionisi, Smith and Kilborne. In 1885 a further advance was 

 made by Golgi, who ascertained that the human parasites pro- 

 pagate within the body of the host by means of ordinary asexual 

 spore-formation ; that the exacerbations of fever in a patient are 

 coincident with the disruption of the clusters of spores produced 

 by the organisms ; and that there are at least three varieties of 

 the parasites in man in Italy. These observations were con- 

 firmed and extended by a large number of persons working in 

 various parts of the world — most prominent among whom 

 are Marchiafava, Celli,. Vandyke Carter, Grassi, Osier, Bignami, 

 Antolisei, Councilman, Mannaberg, Romanowsky, Labbe, Koch, 

 Manson, Thayer and MacCallum. In short, the work of all 

 these observers, and of many others scarcely less meritorious, 

 has not only absolutely established the fact that the parasites 

 are the cause of malarial fever, but has given us a very thorough 

 knowledge both of the parasites themselves and of their path- 

 ological effects, direct and indirect ; until the science of malaria 

 — for it may almost be described as a science in itself — has be- 

 come a brilliant exemplar of the modern methods of research as 

 regards the science of disease in general. 



But I am not here concerned with questions of pathology in 

 malarial fever. At the conclusion of the labours to which I 

 have just referred, we had, it is true, grasped the nature of the 

 disease itself; but a question of the greatest moment still 

 required an answer. We had studied side by side the morbid 

 process and the parasites which cause it ; but we had still to find 

 out how infection is caused, how these parasites effect an 

 entry. We had ascertained the life-history of the parasites 

 within man, and of the kindred parasites within other animals ; 

 but, even after all these investigations, the life-history of the 

 parasites outside man and outside other vertebrate hosts 

 remained to be discovered. Until this was done our knowledge 

 was not complete. It is now my privilege to describe the 

 interesting theories and investigations which led to the solution 

 of this great and difficult problem. 



The importance of the problem need not be enlarged upon. 



1 A lecture delivered at the Royal Institution of Great Britain on 

 March 2, by Major Ronald Ross, D.P.H., M.R.C.S., Lecturer in Tiopical 

 Medicine, University College, Liverpool. 



NO. 1587, VOL. 61] 



In the British army in India during the year 1897, out of a totaP 

 strength of 178,197 men, no less than 75,821 were admitted into 

 hospital for malarial fever ! Fortunately the death-rate of the 

 disease is low in most places ; but on the other hand the cases 

 are so numerous that in the aggregate the mortality fron> 

 malarial fever is very large indeed. For instance, in India 

 alone, among the civil population (who do not take adequate 

 treatment) the mortality from " fevers " during the single year 

 1897 amounted to the enormous total of 5,026,725^over five 

 million deaths — being nearly ten times that due to any other 

 disease. Although undoubtedly thousands of deaths are wrongly 

 attributed to fever in these statistics, such figures can point only 

 to a very great mortality due to malaria. Yet India on the 

 whole is not nearly so malarious as many localities — such, for 

 instance, as places on the coasts of Africa. In short, next per- 

 haps to tuberculosis, malarial fever is admittedly the most 

 important of human diseases. 



I3ut if the problem to which I refer was an important one, its 

 solution presented difficulties which I, for one, formerly thought 

 to be insuperable. It has been mentioned that Lancisi and 

 Pringle connected the disease with stagnant water ; and their 

 views have been generally endorsed by innumerable observa- 

 tions made since their time — by the general experience of man- 

 kind, by statistics, and by the fact that malaria can often be 

 actually banished by means of drainage of the soil. But 

 Laveran had now shown the disease to be due to a parasite of 

 the blood. How reconcile these facts ? There appeared to be 

 but one way of doing so — namely, by supposing that the 

 organism lives a free life in the water or soil of malarious places, 

 from which it enters man by the respiratory or digestive tracts. To 

 prove this it was necessary to discover it in the water or soil of 

 malarious places. But how make this discovery ? The organism 

 is not a bacterium, but an animal parasite. It cannot be taker> 

 from the living blood and sown on the surface of a gelatine film. 

 Experiments have proved that it can be inoculated from mar> 

 to man by the intravenous injection of fresh infected blood ; but 

 this is a very different thing to cultivating it in an artificial 

 medium. At all events, experiments in this line have always- 

 failed and are not in the least likely to succeed. The parasites 

 simply perish when taken from their natural habitation, the 

 blood. It was therefore extremely unlikely that we should 

 ever be able to follow up their life-history by this means — 

 which has proved so successful as regards the bacteria. It 

 remained only to find them in the soil or water by direct 

 search. But how identify them among the host of Protozoa 

 which live in these elements ? Certainly not by their form 

 or appearance. As known to us at that time, they were 

 simply minute amnebx ensconced in the red corpuscles and 

 accurately adapted for such a life. Now red corpuscles do not 

 exist in soil and water ; if the parasites live in the latter, they 

 must possess some other form to that which they possess in the 

 blood, and the clue afforded by identity of appearance fails us. 

 The only remaining method open to us would have been to 

 attempt to produce infection by each one in turn of the 

 numerous species of Protozoa found in the water and soil of 

 malarious places— a task of great magnitude, and one which we 

 now know would have failed. Indeed, it was actually attempted 

 by several observers, and actually did fail. 



Such was the state of things up to the end of the year 1894, 

 Speaking for myself, I can well remember the hopeless feelings 

 with which I then regarded the problem. Fortune, however, 

 was to be kinder to us than I had dared believe. At this very 

 moment the key to the solution of the problem had already 

 been indicated by Dr. Patrick Manson. 



I have said that since the original discovery of Ray Lankester 

 numerous haematozoa — or rather hiemocytozoa — have beer^ 

 found in man and various animals. All these are generally 

 classed by zoologists in Leuckart's order of the Sporozoa, and 

 are usually divided into three groups — groups which are not 

 very closely related, except for the fact that all the organisms 

 concerned are parasites of the red corpuscles of the blood. One 

 group — found in reptiles — consists of parasites closely allied to- 

 the Gregarinidse ; another is found in oxen, and is the cause of 

 Texas cattle-fever ; the third — for which I adopt the name of 

 Hsemamoebidse, Wassielewski — is found in man, monkeys, bats 

 and birds. It is to this third group — the Hsemamoebidse — to- 

 which we must now direct our attention, because it includes the 

 parasites of malarial fever. There are, at least, two knowr> 

 species found in birds, two in bats, one in monkeys, and three 

 in man. The human parasites are those which respectively 



