FEVERS. 559 



our bodies, generating a more considerable degree of cold, which 

 shews its effects in the innermost recesses, in so much that per- 

 sons in their beds in the morning are sensible of the blowing of 

 such a wind. 



"Having thus explained the several modifications of heat and 

 cold by moisture and dryness, I am now brought back to the 

 more particular consideration of these agents. 



" I begin with the effects of cold ; this, by increasing the 

 tonic powers of the simple solids and of the moving fibres, gives 

 a tendency to the Diathesis phlogistica ; and it is in this way 

 that it modifies epidemic diseases, and that inflammatory dis- 

 eases are constantly the produce of these circumstances in cold 

 climates and seasons. It is indeed a certain vicissitude of heat 

 and cold which has the most considerable share, so that these 

 diseases are not so much the production of the winter as of the 

 spring, and are therefore called vernal diseases ; it is the preced- 

 ing cold, however, which gives the diathesis and the characteristic 

 form of the epidemic. 



" Heat dos manifestly relax the arterial system, and, con- 

 trary to the popular notion, makes it less susceptible of the 

 diathesis phlogistica ; and not only does that modification of fe- 

 ver which depends upon the inflammatory diathesis occur more 

 rarely in warm climates, but when it is produced hi the spring to 

 a great degree, the heat of the summer takes off the inflammatory 

 diathesis. But heat also increases the tendency to putrefaction, 

 which is always present in the animal fluids ; so that if the 

 causes of fevers act, a hot state of the air determines them to be 

 of a more putrid kind ; and as heat is the leading circumstance 

 in the production of marsh effluvia, and in giving force and ac- 

 tivity to human contagion, it may be considered as the chief 

 cause which gives occasion to levers ; and from the septic na- 

 ture of the cause, and a concurring state of the fluids, it deter- 

 mines fevers in warm climates to be of the putrid kind, which ac- 

 cordingly is the character of all summer and autumnal diseases. 



" We have thus two classes of epidemics, which comprehend a 

 great number, and will explain Sydenham's division of fevers 

 into vernal and autumnal ; the first of these being considered 

 as inflammatory, and the last as putrid. With regard to this 



