Dr. Mac CuUoch on Malaria on Ship-board. 51 



whatever has been offered of their power in producing these 

 diseases, and that there is not even a probability that they are 

 the real causes which they have so long been supposed, though 

 they may well be aiding ones, either as they render the body 

 more susceptible of the action of these, or as they may be in 

 some cases the very vehicle of the true cause, or the poison in 

 question. And I cannot help thinking that, in any other science 

 than physic, such reasoning would be satisfactory : unfortu- 

 nately, this one has never yet guided itself by the ordinary 

 rules of philosophy, nor been accustomed to the severity of 

 logic ; so that against its modes of faith, philosophy and logic 

 are arrayed in vain. 



But its errors are those of imperfect observation in this 

 case, and are founded on a fallacy which it will not be very 

 difficult to explain. Fevers, non-contagious ones, are proved 

 to be produced where vegetable decomposition abounds most, 

 or is most rapid ; or wherever that unknown substance called 

 Malaria, as contained in the air which has obtained this term 

 from its effects, is present. And such fevers are also proved to 

 increase with the increase and activity of these causes, for- 

 merly explained ; to diminish with their diminution, and to 

 disappear with their disappearance. This in itself approaches 

 to a demonstration that here Ues the real cause : in any other 

 science, in any science which was not governed by phrase- 

 ology and prejudices, it would be considered demonstration. 



But the fallacy becomes plain. All the imaginary causes 

 which I have been discussing, exist everywhere, and they must 

 needs exist, therefore, where malaria does. They can always 

 be traced, while malaria has been neglected ; while, in our own 

 country in particular, the medical world has remained ignorant 

 of it, or has most unaccountably thought fit to forget what has 

 been well known, if never so accurately known as it ought to 

 have been. It is always easy to have recourse to an obvious 

 cause: under the prejudices of physic, those which I have 

 been arguing against have been selected, habitually and tra- 

 ditionally ; and thus those which were but the accessory causes 

 often not even that, have been invested with the title of ori- 

 ginal or true causes. 



Here I think I may drop this subject, leaving these argu- 



E 2 



