SUP. I. 1 1. 6. THEORY OF FEV&R. 479 



time occafion an increafe of the aflbciate motion of another part, 

 which is catenated with it. 



This circumftance neverthelefs can only occur in thofe parts 

 of the fyftem, whofe natural actions are perpetual, and the ac- 

 cumulation of fenforial power on thai account very greai, 

 when their activity is much leflened by the deduction of their 

 ufual ftimulus ; and are therefore only to be found in the fan- 

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

 capillaries. Of the firft of which the following is an inftance. 



The refpiration of a reduced atmofphere, that is of air mixed 

 with hydrogene or azote, quickens the pulfe, as obferved in the 

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

 which Dr. Beddoes adds in a. note, that " he never faw au in- 

 ftance in which a lowered atmofphere did not at the moment 

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

 and arteries." Confiderations on Factitious Airs, by Thomas 

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

 By the afliftance of this new fact the curious circumftance of 

 the quick production of warmth of the Ikin on covering the 

 head under the bed-clothes, which every one muft at fome time 

 have experienced, receives a more fatisfactory explanation, than 

 that which is given in Clafs IV. I. i. 2. which was printed 

 before this part of Dr. Beddoes's Confiderations was publilhed. 



For if the blood be deprived of its accuftomed quantity of ox- 

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

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

 titious air with lefs proportion of oxygen, which in common ref- 

 piration pafles through the moift membranes of the lungs, and 

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

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

 itimulus of oxygen. And as thefe veflels are fubject to perpet- 

 ual motion, the accumulation of the fenforial power of irrita- 

 tion becomes fo great by their leflened activity, that it excites 

 the veflels next connected, the cutaneous capillaries for inftance, 

 into more energetic actions, fo as to produce increafed heat of 

 the (kin, and greater perfpiration. 



How exactly this refembles a continued fever with weak and 

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

 are leflened by defect of the excitement of the fenforial power of 

 aflbciation, owing to the torpor or leflened actions of the ftoni- 

 ach ; hence the accumulation of the fenforial power of aflbcia- 

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

 former, becomes fo abundant as to excite into increafed action 

 the parts moft nearly connected, as the cutaneous capillaries. 



la refpect to the circumftance mentioned by Sydenham, that 



covering 



