28 THEORIES 



might be almost indefinitely multiplied, but the task is 

 unnecessary. 



Hoffman attributed malarious fevers to a lessened elas- 

 ticity of the air. His notion, obscurely conceived and 'in- 

 accurately stated, is only excusable because of the loose 

 philosophy of his day on every subject connected with at- 

 mospheric phenomena. Air is always equally elastic, and 

 any modification of its density, except by adulteration, 

 cannot be very partial for any length of time, so as to 

 create a permanent insalubrity. When adulterated by 

 excessive moisture or unusual gases, it is altered in com- 

 position, a cause of disease much more intelligible than 

 that of mojdification merely of density. 



Particular gases have also been supposed to exert ma- 

 larious influence : Carbonic acid, nitrogen, cyanogen, car- 

 buretted hydrogen, phosphuretted hydrogen, ammonia and 

 all the imaginable effluvia from decomposing organic com- 

 pounds, have had, each, its advocate. As yet, however, 

 no one has been able to show that marshy or insalubrious 

 places abound most, or peculiarly, in such emanations; 

 nor has it been made even probable that any one of these 

 can, or ever did produce an ague ; while we know that in 

 the busy haunts of non-malarial districts, the arts produce 

 indefinitely diversified decompositions and emanations both 

 animal and vegetable, with wonderful impunity to artisans. 



The great difficulties in the way of other theories have 

 induced some authors to suppose that the emanations pro- 

 ductive of fevers result from the action on water of living 

 vegetables, or of vegetables not dead but dying. Others 

 have found more astringent vegetables in hot than in cold 

 climates, and have conjectured that some combination of 

 animal matter with tannin constituted malaria. Not yet 

 satisfied with conjectures, ft few presume that the decom- 



