OF MALARIA. 31 



ure is exhaled, why does it sometimes poison its subjects 

 in a single hour, or make an impression actively expressed 

 sometimes months afterwards? Ferguson has himself ad- 

 duced a fact irreconcilable with his theory, where the army 

 suffered in long droughts when at a distance from porous 

 and wet soils. His hypothesis is also in opposition to the 

 fact that in Africa the greatest mortality is during the 

 rains, when the earth is always drenched with water. On 

 the other hand, the shores of the Mediterranean are most 

 pestilential when a long drought has parched up the earth. 



It would be a waste of time to even enumerate the theo- 

 ries of malaria, founded on the supposition of an unusual 

 disproportion of the ordinary atmospheric elements, such 

 as an excess or deficiency of oxygen or nitrogen, or car- 

 bonic acid, or water. Nor would it be of more use to cite 

 the electrical and magnetic theories of disease, since no 

 analysis of malarious atmospheres has revealed any defect 

 of its elements or of its imponderable constituents. Not a 

 fact sustains any of these opinions, and observations ex- 

 tensively made thoroughly falsify them.* Whatever of 

 change from such causes is observable in malarious places, 

 must be ascribed to their power to excite, not to pre- 

 dispose. 



The only theoretic view of malaria to which I incline, 

 is that which refers marsh fevers, and some of the epi- 

 demic diseases, to a living organic cause, capable of repro- 

 duction by germs, as is alleged of contagious diseases; 



* M. Peltier, by constant observations, found the clouds in 1835 almost 

 always positive, in 1836 generally neutral or negative, yet no marked dif- 

 ference in health was observed in those years. 



Since these lectures were written, Sir James Murray has defended with 

 much ability, the electrical theory of malarious and epidemic diseases. 

 (Lancet, Oct. 1848.) 



