1900.] on Malaria and Mosquitoes. 17 



that the parasite is an organism which in its free state dwells in such 

 places, and diffuses itself in such mists. It is interesting to note 

 how near to the truth this almost instinctive conception took us. It 

 is right in idea, wrong in fact. It is not the parasite itself which 

 springs from the marshy ground, but the carrier of the parasite. 



This was one of the many interesting points made by King in his 

 mosquito-theory of seventeen years ago. But King fell into an error 

 which could have been used as a powerful argument against his 

 hypothesis. He seemed to have assumed that all mosquitoes rise 

 from marshes. Hence, he said, malaria exists in the presence of 

 marshes ; hence it is a disease of the country, rather than of towns, 

 and so on. As a matter of fact, mosquitoes as a rule do not rise from 

 marshes at all ; they do not all even rise from pools of water on the 

 ground ; the commonest species, at least of those which habitually 

 annoy human beings, spring from tubs and pots of water in the 

 vicinity of houses, and are indeed more common in cities than in 

 country places, at any rate in the tropics. Now it is not the least 

 interesting feature of recent researches that they have shown where 

 the error lay. As soon as I have succeeded in cultivating the human 

 parasites in my " dappled-winged mosquitoes," which were really 

 gnats of the genus Anopheles, I began to study the habit.s of these 

 insects, and soon ascertained the remarkable fact that while gnats of 

 genus Culex generally breed, in India, in vessels of water round 

 houses, gnats of genus Anopheles, which I had just connected with 

 malaria, breed in small pools of water on the ground. This point was 

 made the subject of a special investigation by the recent expedition 

 to Sierra Leone ; and we found that the law holds good there as in 

 India. While Culex larvaa wore to be seen in almost every vessel of 

 water, or empty gourd or flower-pot in which a little rain-water 

 collected, in only one case did we find Anopheles larvae in such. On 

 the other hand, Anopheles larvae occurred in about a hundred small 

 puddles scattered through the city of Freetown puddles mostly of a 

 fairly permanent description, kept filled by the rain, and not liable 

 to scouring out during heavy showers. What was almost equally 

 significant, the larva) seemed to live chiefly on green water-weed. 

 Hence it follows that while Culex, the apparently innocuous genus 

 of gnats, are essentially, or at least often, domestic insects, Anopheles, 

 the malaria-bearing genus, are essentially gnats which spring from 

 stagnant water on the ground. And numerous other facts in the 

 history of malaria can be explained by the same discovery. It is 

 supposed, for instance, that malaria originates from freshly-turned 

 earth ; now we actually noted examples where railway embankments 

 and the like had produced Anopheles pools ; and it is easy to see that 

 disturbance of the soil may often produce depressions in the ground 

 capable of holding a little rain-water suitable for the larva? of these 

 insects. Again malarial fever often appears on board vessels which 

 have touched at malarious ports ; as an explanation of this we ascer- 

 tained that Anopheles visit ships from the shore. In short, on study- 



