On the Relations between Mind and Muscle. 1 69 



movements in the function alluded to are occasioned by a sensation of dis- 

 tress, and a consequent desire of relief produced by the venous blood in 

 the lungs 5 but there is no evidence from consciousness that in ordinary 

 respiration any such sensation does actually take place. It is true that 

 when an obstacle is presented to the aeration of the blood, we for the most 

 part experience uneasy feelings, which are followed by voluntary exertions 

 of the accessory muscles of respiration : but in that kind of respiration which 

 is commonly going on, and frequently when consciousness is altogether 

 suspended, or occupied with other subjects, all that we know«of the causa- 

 tion of the muscular action, amounts to nothing more than that black blood 

 reaches the lungs, and that the diaphrogra descends j and we have as much 

 reason to say that the former event is the stimulus of the latter, as that 

 blood is the stimulus to the contraction of the heart; the only difference 

 being, that the influence of the black blood in the lungs upon the move- 

 ments of the diaphragm, is probably transmitted by nerves. 



2. We pass on to the second head,* which comprehends many interesting 

 actions, and among them certain kinds of respiration, which are frequently 

 cliaracterized as voluntary, though possessing no title to that designation. 

 Respiration does not become voluntary till a feeling of desire has arisen 

 for increasing the action, or for overcoming an impediment to its exercise ; 

 but on many occasions, uneasy sensations in the chest occur, and are fol- 

 lowed by an increase of respiratory movement, without any mental feeling 

 amounting to will or desire ; as for instance, in those occasional muscular 

 contractions which constitute sneezing, sighing, coughing, laughing, yawn- 

 ing, &c. and which all belong to the class respiratory. A tickling sensa- 

 tion in the nose causes sneezing ; a sensation of weight about the lower 

 part of the chest, sighing ; an irritation in the windpipe, coughing ; and in 

 each case the action instead of being prompted by the will or desire, takes 

 place in direct opposition to it. We shall content ourselves with merely 

 hinting at these instances, in order that we may have more time for con- 

 sidering certain other interesting movements which belong to the present 

 head j those, namely, which are employed in preserving the balance of the 

 ,bodj'. 



Every one by experience knows both the feeling of equilibrium, and the 

 fear of losing it. Yet there is nothing more worthy of admiration in the 

 whole animal econoniy, than the fact, tliat without any knowledge of the 

 centre of gravity, or of its situation in the body, or of the law by virtue 

 of which a body must fall, if a perpendicular from the centre of gravity 

 passes outside of the base of support, a person shall notwithstanding ex- 

 perience a sensation which gives him an apprehension of falling, whenever 

 the centre of gravity is lost; but when we consider that this sensation 

 is immediately followed by instinctive motions, which tend to recover the 



* Motions consequent upon internal sensations. 



