"The first shipload [of European labourers] arrived during the dry season, when mosquitoes were most scarce, and were quartered in unscreened buildings. Within six weeks of their arrival 33 per cent. of these labourers had been taken sick with malaria. The second shipload arrived during the rainy season, and were quartered in a camp not 200 yards distant from that of their predecessors. The buildings of the camp were screened. Sickness among the men was infrequent, and when they had been upon the Isthmus six weeks it was found that only 4 per cent. had found their way to the hospitals." * * * * * The destruction of larvæ, and of their hiding places, is commenced by the clearing of grass and bushes, which are cut down with the _machete_, a short cutlass with which the Panamanian is very expert, _machete_ work being, indeed, the principal _rôle_ in which the Panamanian is employed by the Commission. Also ditches are cleaned out, and heavy oil poured upon the water in trenches and pools, and land-crabs are caught and the holes in which they dwell are filled in or oiled. Finally the soil is drained, which is the only means of making the ground permanently unfit for mosquito breeding. Subsoil draining is the best, a tile drain being put in; for, even in concreted gutters, pools will form, owing to accidental obstruction, and remain sufficiently long for the deposition and hatching of the larvæ. Such is the work of the _anopheles_ brigade, and the _stegomyia_ brigade carry out similar operations, in the neighbourhood more particularly of Panama. With regard to the effect of these operations upon the numbers of the mosquitoes I may narrate my own experience. I arrived at Colon first in January, 1907, and spent one or two nights on board my ship. This was two years and a half after the commencement of the mosquito campaign, and the officers of the ship congratulated themselves upon the absence of the swarms of mosquitoes which formerly attacked them at night on their vessel. I found, however, that although there was no swarm of mosquitoes, such as I have seen, _e.g._, when on board ship in the harbour of Colombo, Ceylon, yet that the individuals who remained certainly caused me discomfort, and I think some subsequent indisposition. In April, 1908, however, during two days at Colon, I did not so much as see a single mosquito. [Illustration: LOOKING NORTH FROM RAILWAY BRIDGE AT PARAISO.] [Illustration: ABANDONED FRENCH MACHINERY.]