INSECTS AND DISEASE. 647 



would carry it out to sea, the water will form a barrier to its farther 

 progress seaward, for it is not a marine insect. Mosquitoes, therefore, 

 accumulate on sea-coasts notably at some of our familiar summer re- 

 sorts, Cape May, Atlantic City, etc. 



5. Malaria " has an affinity for dense foliage, which has the power 

 of accumulating it when lying in the course of winds blowing from 

 malarious localities." 



6. " Forests or even woods have the power of obstructing or pre- 

 venting its transmission under these circumstances." 



These last two propositions, embodying, first, the " accumulation," 

 and, second, the " obstruction," of malaria by forests and trees, may be 

 considered together. That a wind coming from a marsh (from, in fact, 

 a mosquito nursery), and bearing a colony of mosquitoes, should be 

 screened or sifted of its insect burden by passing through the foliage 

 of a forest, or a belt of trees, is certainly far more comprehensible than 

 the conception of a malarial vapor being so screened by virtue of its 

 " affinity for foliage." And though, in the case of a single belt of 

 trees, even the mosquital filter may appear imperfect, the insect, should 

 it have been carried far, is probably anxious to settle, and may so 

 vary its course by steering as to take the first opportunity of clinging 

 to anything that may come in its way; and, having settled, we may 

 readily conceive its shifting round to the leeward side of a leaf or 

 branch, and there holding on until the wind sufficiently subsides to 

 allow of safer flight. Thus mosquitoes, "like malaria, may both accu- 

 mulate in, and be obstructed by, forests and trees. 



The conduct, or rather the mechanical properties, of the mosquito, 

 when carried by the wind, can hardly be better described than in the 

 following verbatim quotation from Sir Francis I)ay, in his description 

 of malaria. He says : " Malaria may be carried by the winds to places 

 where it was not generated ; it is obstructed by and hangs in the foli- 

 age of trees, or in mosquito-curtains ; it subsides into low places, and 

 may be blown over a hill, and, may be very virulent on the side oppo- 

 site to that on which it was formed. In like manner it may be taken 

 up the side of a hill, and, as a lull takes place in the atmosphere, con- 

 sequent upon its weight it rolls down, and may thus envelop its base 

 with a deadly belt of fever, for there, hanging in the leaves of the 

 trees, it gradually sinks through them to the earth beneath, in which 

 situations it is most dangerous to pass the night " (Sir Francis Day's 

 work, p. 87). 



7. "By atmospheric currents it" (malaria) "is capable of being 

 transported to considerable distances, probably as far as five miles." 

 So, certainly, is the mosquito. 



8. " It " (malaria) " may be developed in previously healthy places 

 by turning up of the soil, as in making excavations for the foundations 

 of houses, tracks for railroads, and beds for canals." Here two things 

 are confounded, viz. : 1. Turning up of the soil, as by plowing or dig- 



