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through the medium of the nerves having been ascertained), yet I 

 suspect there are some points which have either not been thought 

 upon or are at least not determined, and may therefore be proposed 

 as questions. 



1st, Is the descent of the diaphragm in the first and subsequent 

 inspirations mechanical? that is, does the pressure of the air cause it 

 to descend, or does it descend by an inverted contraction of those 

 fibres which produce its ascent! or, 



2nd, Are these two acts, viz. inspiration and expiration, pro- 

 duced by the contraction of two sets of muscular fibres ? The most 

 obvious solution of this matter seems to be, that the fibres of the 

 diaphragm contract only in the act of expiration, that their power of 

 contraction is spent by each exertion of it, and that having con- 

 tracted their full sphere, the resistance to the pressure of the air 

 ceases, and this medium entering the lungs, distends them and de- 

 presses the passive diaphragm, which having attained a certain 

 point, re-acts and expels the air. Thus far the theory: then, arising 

 out of it, it is to be asked, 



3rd, What share has the pressure of the air or the distension of 

 the lungs in producing a contractile movement of the muscular 

 fibres? It will be pertly answered to this question, the stimulus of 

 pressure or disteution causes the diaphragm to contract. Let it then be 

 called a stimulus, since we must designate the agent by some name. 



4th, What then is the relation of this stimulus with the power of 

 contraction? is there a property belonging to pressure or distention, 

 directly related with the animal properties of the structure ? or is 

 the relation mediate; that is, by the intervention of mechanical 

 properties of the texture, related with the vital ones? These points 

 settled, it remains to be determined concerning the relations by 

 which the act of contraction is constituted ; as, 



5th, Whether the properties related with this stimulus of dis- 

 tention, and concurring with it to produce the contraction, live by 

 assimilation in the structure of the respiratory muscles,? or whether 

 they are obtained from a distant source? The latter appears to 

 have been ascertained by the results of the division of nerves, &c. 

 This conclusion admitted, 



6th, Are those properties of the respiratory muscles derived 

 from a distant source, regularly and unremittingly communicated 

 while the nerves are unimpaired ? or are they of the occasional kind, 

 that is, produced in the muscles by a process of the following order : 

 1. Foreign properties (the stimulus of distention) related with and 

 producing change of the inherent ones of the muscles. 2. This 

 changed condition of the inherent muscular properties related with 

 others belonging to the nervous centres. 3. Effect of this rela- 

 tion, that properties from the centre (under this process) are com- 

 municated to the distant muscles. 4. Conjoint result of all these 

 properties, a contraction of the muscular fibres? These questions 

 belonging to mechanical respiration, are here merely suggested, 



