SUP. I. 11. 6. THEORY OF FEVER. 479 



time occasion an increase of the associate motion of another part, 

 which is catenated with it. 



This circumstance nevertheless can only occur in those parts 

 of the system whose natural actions are perpetual, and the ac- 

 cumulation of sensorial power on that account very great, 

 when their activity is much lessened by the deduction of their 

 usual stimulus; and are therefore only to be found in the san- 

 guiferous system, or in the alimentary canal, or in the glands and 

 capillaries. Of the first of which the following is an instance. 



The respiration of a reduced atmosphere, that is, of air mixed 

 with hydrogene or azote, quickens the pulse, as observed in the 

 case of Mrs. Eaton by Dr. Reynolds and Dr. Thornton; to 

 which Dr. Beddoes adds in a note, that " he never saw an in- 

 stance in which a lowered atmosphere did not at the moment 

 quicken the pulse, while it weakened the action of the heart 

 and arteries." Considerations on Factitious Airs, by Thomas 

 Beddoes and James Watt, Part III. p. 67. Johnson, London. 

 By the assistance of this new fact, the curious circumstance of 

 the quick production of warmth of the skin on covering the 

 head under the bed-clothes, which every one must at some time 

 have experienced, receives a more satisfactory explanation, than 

 that which is given in Class IV. 1. 1.2. which was printed be- 

 fore this part of Dr. Beddoes's Considerations was published. 



For if the blood be deprived of its accustomed quantity of oxy- 

 gen, as in covering the head in bed, and thus breathing an air 

 rendered impure by repeated respiration, or by breathing a fac- 

 titious air with less proportion of oxygen, which in common re- 

 spiration passes through the moist membranes of the lungs, and 

 mixes with the blood, the pulsations of the heart and arteries 

 become weaker, and consequently quicker, by the defect of the 

 stimulus of oxygen. And as these vessels are subject to perpe- 

 tual motion, the accumulation of the sensorial power of irrita- 

 tion becomes so great by their lessened activity, that it excites 

 the vessels next connected, the cutaneous capillaries for instance, 

 into more energetic actions, so as to produce increased heat of 

 the skin, and greater perspiration. 



How exactly this resembles a continued fever, with weak and 

 quick pulse ! in the latter the action of the heart and arteries 

 are lessened by defect of the excitement of the sensorial power of 

 association, owing to the torpor or lessened actions of the sto- 

 mach; hence the accumulation of the sensorial power of associa- 

 tion in this case, as the accumulation of that of irritation in the 

 former, becomes so abundant as to excite into increased action 

 the parts most nearly connected, as the cutaneous capillaries. 

 In respect to the circumstance mentioned by Sydenham, that 



