105 



inind is directing that process ; and from the em- 

 barrassments opposed to the natural action of the 

 respiratory organs by the contrivances adapted to 

 them. 



87. It will not be denied, that the size and capa- 

 city of the chest must, in a certain degree, regulate 

 the quantity of air which is taken into or expelled 

 from it ; and since respiration is neither wholly a 

 voluntary nor an involuntary act, but within certain, 

 limits partakes of the nature of both, and is carried 

 on by the exertion of muscular powers, the bulk of 

 respired air must vary also, either from an altera- 

 tion in the action of these powers, or from a change 

 in the will of the agent who exerts them. This 

 may be illustrated by considering the different quan- 

 tities of air taken into the lungs in different states of 

 natural and forced respiration. Dr Goodwyn, sup- 

 posing a person at death to make a complete expira- 

 tion, endeavoured to ascertain the bulk of air then 

 remaining in the lungs, which he estimated at 109 

 cubic inches *. This estimate he fornfed by measuring 

 the capacity of the chest, in subjects who had died a 

 natural death by disease, previous to which the ex- 

 piratory powers must have been much weakened, and 

 unable, in consequence, to expel so much air as 

 when in a state of health and vigour ; and in such 

 cases, therefore, expiration might be final without 

 being complete. Mr Cruickshank observes, accord- 

 ingly, that the lungs in the dead body, (though ex- 

 piration is the last action of life), always retain more 



Connexion of Life with Respiration, p. 27* 



