Dr. Mac Culloch on Malaria on Ship-board, 63 



the calentures, (calentura) as they were formerly termed, of 

 which we read in our old voyages under these circumstances. 

 Such an event will happen chiefly under leeward positions as 

 to the vessel, and of course will occur with land winds, where 

 there are winds of this nature on any shore. And it is also 

 evident how this will occur chiefly at night ; because this is 

 not only the period of the land wind, but because the mere in- 

 fluence of evening and morning, or of night altogether, in the 

 production or propagation of malaria is very considerable, as I 

 have elsewhere shown. Thus chiefly we explain the effects of 

 dews in these climates, as the vehicle of the poison. And if a 

 ship is ever so situated as to the land, as to have her decks 

 covered with dew in the morning, that is in itself a proof that 

 she is within the reach of danger, and ought to be moved ; 

 while I need not say that such dews are actually the perpetual 

 causes of fever to the men of the night watches. And here 

 also we may see the necessity of reducing those watches to the 

 least possible number of men, if the circumstances of the ship 

 do not allow her to leave her position, or weigh and stand out 

 to sea at night. ^ 



And as to the land wind, I may give one general rule appli- 

 cable to all circumstances of ships engaged in tropical climates, 

 or in warm ones generally. It is always attended by that smell 

 of land which is better known than it is easy to describe, and 

 which many delicate or experienced individuals can perceive 

 at great distances. And while I have no doubt, from the facts 

 and reasonings given in the Essay on Malaria, that this sub- 

 stance can be conveyed as far as the smell of land is percep- 

 tible, it would be prudent, whenever that can be done, in such 

 a climate, to weigh and run to sea, and particularly, of course, 

 during the night, when the danger is augmented. And there 

 are circumstances in which a vessel should not even wait for 

 the breeze, but be at least a-trip and ready to get under weigh 

 at the instant it comes to blow ; since in one instance which I 

 have noticed in that essay, in these very circumstances, and 

 even where the captain of a frigate was habitually attentive to 

 this precaution, to such a degree indeed as to order all the su- 

 perfluous men below on this shift of wind, the armourer was 

 seized with the fatal cholera, in the very act of clearing an 



