62 Dr. Mac CuUoch on Malaria on Ship-hoard, 



adopted ; and there is none : while much toil and inconveni- 

 ence also are often incurred in attempting to control an ima- 

 nary contagion. The great object of this paper therefore is to 

 point out those causes, that they may be removed, and with 

 that, such diseases prevented ; and if it was first necessary to 

 explain the differences in fevers, and to show how easily mis- 

 takes must arise, that object is now sufficiently accomplished. 



There are two great and distinct causes whence ships are 

 exposed to malaria ; while if the one has been long familiar, 

 serious errora have nevertheless taken place as to the power of 

 this, and as to the modes in which the danger was incurred. 

 The other has never, as far as I can discover, been pointed out 

 in any medical or other writings, till it was indicated in the 

 Essay on Malaria ; while, from being the least suspected, and 

 from its power of occurring in any ship, in any climate and 

 season, and even at sea, it is the most important one. Against 

 both, precautions are necessary ; and against both, they are 

 available; while, for both cases, they are different. I must 

 explain both here in somewhat greater detail than I did in the 

 Essay on Malaria, for the purpose of the two distinct sets of 

 regulations which ought to be founded on them for the objects 

 of prevention. 



Communication with the shore, in a climate or country pro- 

 ductive of malaria, is the cause generally known to medical 

 men as generating fevers in ships. But the error here has 

 chiefly been that of not attending to the distance to which this 

 influence extended; practically also, that of neglecting such 

 precautions in ordinary cases, as ought to be well known : 

 which, in fact, are known, but are passed over from thoughtless- 

 ness, or from want of recent writings urging, or repeating that 

 which many have forgotten, and others have not acquired. 



I have shown distinctly, that malaria is currently propagated 

 to distances of at least three miles ; and I have given ample 

 reason to believe, in the Essay on Malaria, (I mean in the 

 book itself,) that this influence is very far more widely effective. 

 I have indeed decidedly ascertained since, the instantaneous 

 production of fever through a land breeze, at five miles, to a 

 ship at anchor. Thus it is, apparently, that fevers occur so 

 commonly in ships on nearing the tropical lands ; and hence 



