532 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



engaged the attention of the learned in all ages ; and yet the snh- 

 ject is an open one, and seems to be as for from being settled as 

 ever. 



For some forty years of my life I have lived in truly malarious 

 districts, and have seen and felt ranch of the intermittents and the 

 thousand concomitant forms of diseases, having their origin in the 

 malarious influences, be its intrinsic or essential nature whatever 

 it may. Under the observation and experience thus derived, an 

 hypothesis has, for many years, occupied my mind, which is quite 

 at variance with the several theories usually supported, all of which 

 assume the presence of some si^eciiic poison, or deletenous matter 

 in the atmosphere. 



This hypothesis consists in the supposition that malarious dis- 

 eases are produced, not by any specific poison in the atmosphere, 

 originating from the decomposition of vegetable matter, or any 

 other generating agency, or from the existence of effluvia, or mias- 

 matic emanations of any kind, but from a cause which may be con- 

 sidered as negative, in its character, viz., the want of the normal 

 depuration of the animal organism. 



It is well known that all the tissues are continually undergoing 

 change, by assimilation and defecation. The matters, therefore, 

 which have served their purpose and become effete, rauot be regu- 

 larly expelled, or they act as a virulent poison, and readily become 

 the occasion of great and general disturbance. 



Among the most important of the functions, by which the depu- 

 rative process is performed, is that of perspiration. The exhaling 

 vessels of the skin are ordinarily capal)le, by their vital energies, 

 of presenting the perspirable matters to the surface, and, under 

 the stimulus of either great warmth or exercise, of actually throw- 

 ing them out in the form of sweat ; but in the absence of such 

 stimuli another auxiliary is required, viz., an atmosphere having 

 an affinity for the exhaling matters. In a healthy state of the 

 atmosphere, such affinity is an active, positive force of great power, 

 but it may be stated in various ways, the most simple and common 

 of w^hich perhaps is the evaporation of simple water, which some- 

 times occurs to such an extent that the temperature of the atmos- 

 phere and the dew point are brought to close approximation to 

 each other ; hence the well known danger of being in the open 

 air when the due is formino- around us. 



An excess of carbonic acid, too, has a powerful effect in satisfy- 

 ing the appetency with Avhich the atmosiDhere is otherwise endowed, 



