Dr. Mac CuUoch on Malaria on Ship-hoard. 47 



principles is weakened, and the results that might have been 

 derived from them become more doubtful. In the case before 

 us, it is most essential to ascertain, if this can be done, that, 

 next to contagion, there is no other cause of fever than mal- 

 aria ; because we have then acquired a sure knowledge, at 

 least, as to the mode of prevention, if not an absolute power 

 in this matter. If, for example, in a ship we can control 

 contagion, and if, in the same case, we can equally remove 

 malaria, or its action, there can be no fevers in ships, because 

 we have laid our hands on the only causes. 



Absolutely to prove what I myself believe on this subject, 

 is not possible ; because it is an attempt to prove a negative 

 in a science which is not an accurate one, and because it is an 

 attempt to oppose established habits and prejudices^ in a 

 branch of knowledge which is especially governed by them. 

 All that I can do, is to approximate the facts in as simple and 

 logical an order as I can, and trust the effect to those who are 

 in the habit of weighing moral probabilities ; for of this nature 

 is the present argument. 



The power and effect of malaria are admitted : of this one 

 cause of fever there is no doubt; but it is the custom in physic 

 to say, that they are produced also by heat, or by cold, or by 

 either of these united to moisture ; or, further, by fatigue, 

 errors or deficiency of food, the passions of the mind, and 

 some few other causes, inducing what physicians call de- 

 bility. 



If it is a maxim in philosophy that superfluous causes ought 

 not to be assumed, it is here worthy of remark, that all these 

 causes of fevers were proposed or invented in the ignorance 

 and infancy of physic ; and when the very existence of such a 

 subject, chemically, as malaria, was so little suspected, that 

 the influence, even of marshes, was attributed to moisture, 

 heat, putrefaction, animalculae in the air, defective elasticity 

 in the atmosphere, and any thing else which admitted of 

 some well-sounding term. 



It is also not an unimportant remark here, that to these very 

 same causes, enumerated as the causes of fevers, were attri- 

 buted inflammations, and, indeed, all other diseases. Mankind 

 is naturally inclined to causation ; and in this case physic has 



