48 Dr. Mac Culloch on Malaria on Ship-board. 



mustered everything which could be supposed capable of affect- 

 ing the human body, hoping, perhaps, that if one failed, it 

 was sure of at least including the real cause in the crowd. 

 And, in fact, these words have always been used as a mere 

 string of terms ; not one definite idea having been attached to 

 them, nor to their supposed powers of action : they are but a 

 portion of that phraseology which has ever been the substitute 

 for philosophy in physic ; and not a very uncommon substi- 

 tute also for reasoning in moral science. It is of some value, 

 in such a case as this, to trace the origin and character of 

 opinions ; as we may thus often shake the structure which we 

 cannot directly demolish. 



If a single cause were always the sole agent in producing 

 disease, there would be no difficulty in proving that not one 

 of these was the cause of marsh fever, or of fever that is not 

 contagious. Unfortunately, the condition of the subject to be 

 acted on must also be taken into the account ; as there are 

 predisposing as well as exciting causes. And these last being 

 sometimes obscure and unknown, while the former may be 

 obvious, physic has not unnaturally committed the error of 

 taking up with what was most obvious ; while, in this case, 

 ignorant or neglectful of the presence and power of malaria in 

 all those least obvious instances which I have pointed out in 

 that Essay, it has attributed to heat, or cold, or fatigue, or 

 what not, as prime causes, that power which they possess but 

 as secondary and assisting ones. 



But as the very nature of this question does not allow me 

 to prove the nature of the cause from any single fact, we must 

 try to produce, from a wide mass of such, what could not be 

 deduced from individual or separate ones ; and should this be 

 practicable, the proof is legitimate, because it is only thus that 

 philosophy, in almost any case, arrives at truth. If I can 

 prove that the one cause which is here assumed as the true one, 

 acts as often as it is called into action, and that the power of 

 the others is irregular and uncertain, as also that, in very plain 

 cases, they do not act at all when present ; and further, that 

 when they do appear to be the agents, that other demonstrated 

 cause is also present, or probably existent, it appears to me 

 that the point in question is proved as perfectly as anything 



