32 
REPORT OF THE MALARIA EXPEDITION. 
in the tropics. They have no particular connection with swampy ground, level ground, or 
decaying rock. They are not particularly encouraged by rain, by digging, or by embankments. 
They are not removed by cultivation or surface drainage ; while they swarm in cities. Hence 
we may almost venture to aver that if pot-breeding gnats could carry malarial fever, almost all the 
phenomena of the distribution of the disease would be different from what they are known to be. 
That is, the disease would be most prevalent in cities ; would have no particular connection with 
marshes and level ground, or decaying rock, or rain, excavations, or embankments ; and would 
certainly not be removable by surface drainage. In short, it would certainly be present where it 
is not present, and absent where it is not absent. 
It will be seen from Section IV. that these considerations would seem to exculpate a large 
number of species of Culex which frequently, if not always, breed in vessels of water. 
They would also exclude most other suctorial insects, such as fleas, bugs, lice, etc. 
They would not, however, exclude other suctorial insects which, like Anopheles^ breed 
exclusively or almost exclusively in pools of water. It is impossible, without more study, to say 
how many such insects exist. Certainly some species, even of Culex, can often breed in pools 
of water. 
The Indian observations with " grey mosquitoes " {Culex pipiens type) and " brindled 
mosquitoes" [Culex taniatus type) all proved negative with the luiman parasite — with the doubtful 
exception of one individual. The experiments were very numerous, and the feeding was done 
under natural conditions in mosquito nets \^paragraph 20\ 
The Italian observers record negative results with Italian Culex. 
Koch, however, thinks that Culex may possibly be involved [ii]. 
On the other hand, some nine species of Anopheles, existing in widely separate parts of the 
world, have already been incriminated. 
To sum up, while it seems improbable, or indeed very improbable, that the common pot- 
breeding species of Culex are involved, it is scarcely safe as yet to exculpate the genus entirely. 
Observations regarding other gnats and insects which breed in puddles are still required. But on 
the whole it appears more probable that only gnats of the genus Anopheles are concerned in the 
propagation of human malaria. 
23. Are other Vertebrates besides Man hospitable to the Human Haemamoe- 
bidae ? — Dionisi records [24] that the two species of parasites found by him in bats are 
morphologically very similar to H. prcecox and H. malaria ^ and Koch says [li] that the parasite 
found by him in monkeys is like H. v'lvax. These parasites may perhaps be identical with the 
human species. 
The parasites of birds can scarcely be communicable to man, being too dissimilar to the 
human ones. Exhaustive search in the blood of other mammals besides bats and monkeys is still 
required. In many places dogs are popularly supposed to get malarial fever. 
The Indian experiments showed that H. rel'tcta of sparrows can be conveyed by C.fat'tgans 
to crows and weaver-birds. Reasoning from analogy, then, we may suppose that the human 
