16 Major Ronald Ross [March 2, 



again unsuccessful until he used a number of Anopheles claviger, 

 brought from a house containing infected persons. The result was 

 successful, the subject of the experiment becoming infected after some 

 time. This important experiment gave the first confirmation with 

 human malaria of my previous inoculation experiments with the 

 malaria of birds ; bat since other species of gnats as well as 

 A. claviger had been employed, it failed to fix suspicion entirely on 

 the latter. In order to obtain this result, these observers were finally 

 obliged to resort to the correct method of Manson and myself 

 namely that of direct cultivation of the parasites in the gnat. Success 

 was now immediate. The zygotes and blasts of the parasites were 

 found, exactly as previously described by me, in the tissues of 

 A. claviger ; and lastly, healthy persons were infected by the bites of 

 these insects. Pushing forward with admirable rapidity, the Italian 

 observers next found that all three species of the human Haemamoebidffl 

 are cultivable in A. claviger ; and not only in this, but in other 

 Italian species of Anopheles, while, like me, they failed in cultivating 

 the parasites in Culex. 



Almost simultaneously Koch repeated and confirmed with the 

 weight of his authority most of the results which had been obtained 

 as regards both the human and avian parasites. In August 1899, the 

 malarial expedition sent to Sierra Leone by the Liverpool School of 

 Tropical Medicine (of which expedition I was a member), found the 

 human parasites in two species of Anopheles in that colony, namely 

 A. costalis, Loew, and A. funeslus, Giles. I hear also that the same 

 result has been obtained with Anopheles in two other parts of the 

 world, so that it would appear that something like nine species of 

 Anopheles have now been inculpated while as yet every species of 

 Culex which has been tried has failed to give positive results. 



From this point it becomes impossible to follow in detail the 

 researches carried out in connection with the mosquito theory in 

 various parts of the world. The facts already collected would fill 

 a small volume ; and every month witnesses additional publications 

 on the subject. I shall therefore, in conclusion, content myself with 

 a brief reference to three points of leading importance. 



I shall first try to indicate how completely the recent discoveries 

 explain the well-known laws regarding the diffusion of malaria. As 

 mentioned at the beginning of this lecture, malarial fever has long 

 been known to be connected with the presence of stagnant water. 

 That is to say, we generally, though not invariably, nud that the 

 disease is associated with low-lying flat areas, where water tends to 

 collect to a considerable extent. It was indeed the general apprecia- 

 tion of this law which led to the old miasma-theory of the disease 

 the theory on which the word " malaria " was based. We assumed 

 that the poison is one which rises from marshy areas in the form of 

 a mist, and which thence infects all living within a given distance. 

 Later, when the pathogenetic parasite was discovered in the blood of 

 febricitants, many observers, still clinging to this conception, thought 



