FEVERS. 493 



it will be the proper place for considering this matter more fully ; 

 and I hope I shall be able to make it evident, that the produc- 

 tion of spasm, even there, will admit of an explanation upon 

 the system I have laid down, and will be found to depend upon 

 a previous debility, or something analogous to it." 



XXXVIII. How the state of debility produces some of the 

 symptoms of the cold stage, may perhaps be readily explained ; 

 but how it produces all of them, I cannot explain otherwise than 

 by referring the matter to a general law of the animal economy, 

 whereby it happens, that powers which have a tendency to hurt 

 and destroy the system, often excite such motions as are suited 

 to obviate the effects of the noxious power. This is the vis me- 

 dicatrioo naturae, so famous in the schools of physic ; and it 

 seems probable, that many of the motions excited in fever are 

 the effects of this power. 



XXXIX. That the increased action of the heart and arteries, 

 which takes place in the hot stages of fevers, is to be considered 

 as an effort of the vis medicatrix naturae, has been long a com- 

 mon opinion among physicians ; and I am disposed to assert, 

 that some part of the cold stage may be imputed to the same 

 power. I judge so, because the cold stage appears to be uni- 

 versally a means of producing the hot ; because cold externally 

 applied has very often similar effects. " If a man is suddenly 

 plunged into cold water, taken out trembling and shaking, and 

 put to bed, he will become preternaturally hot and even sweat, 

 and hence have all the symptoms of an ague." And more cer- 

 tainly still, because it seems to be in proportion to the degree 

 of tremor in the cold stage, that the hot stage proceeds more or 

 less quickly to a termination of the paroxysm, and to a more 

 complete solution and longer intermission. (See XXX.) 



XL. It is to be particularly observed, that during the cold 

 stage of fever there seems to be a spasm induced every where 

 on the extremities of the arteries, and more especially of those 

 upon the surface of the body. This appears from the suppres- 

 sion of all excretions, and from the shrinking of the external 

 parts ; and although this may perhaps be imputed in part to 

 the weaker action of the heart in propelling the blood into the 

 extreme vessels, yet as these symptoms often continue after 

 the action of the heart is restored, there is reason to believe that 



