IRRITABILITY, AND MUSCULAR POWER. 



109 



Books in the running brooks, 

 Sermons in stones, and good in every thing— 



this, perhaps, might be the part of creation which we could best select in proof 

 of the wisdom of the Creator. 



It was formerly too much the custom to regard the animal frame as a mere 

 mechanical machine ; whence, in that spirit of absurdity with which the 

 wisest of mankind are occasionally afflicted, Descartes affected to believe 

 that brutes are as destitute of consciousness as a block of wood, and that it 

 is exactly the same sort of necessity which drives a dog forward in pursuit 

 of a hare, that compels the different pipes of an organ to give forth different 

 tones upon a pressure of the fingers aganist its different keys. It is not every 

 one, however, in modern times who has adopted the mechanical theory that 

 has carried it to this extremity of absurdity ; but all of them are still carry- 

 ing it too far who reason concerning the principal motions of the body as 

 mere mechanical motions, and the powers which the muscles exert as mere 

 mechanical powers ; in which the bones are the levers, the joints the fulcra, 

 and the muscles the moving cords ; for it so happens that all the effects for 

 which the whole of this complicated machinery is absolutely necessary out 

 of the body, are in many instances performed by a single part of it within 

 the body, namely, by the moving cords or muscles alone, without either bones 

 or joints, levers or fulcra. I do not mean to contend that there is no kind 

 of resemblance or conformity of principle between the laws of animate and 

 inanimate mechanics, for I well know that in a variety of points the two sys- 

 tems very closely concur ; but I am obliged to contend that they are still two 

 distinct systems, and that in the one case the living power exercises an influ- 

 ence which finds no sort of similitude in the other. 



It is, indeed, curious to observe the difference of result which has flowed 

 from the calculations of the different promoters of this theory ; and which 

 alone, were there nothing else to oppose them, would be sufficient to prove 

 the fallacy of their reasoning. Among those who have adopted this mode 

 of explanation, and have pursued it with most acuteness, and may be re- 

 garded as the fathers of the school, I may be allowed to mention Borelli and 

 Keil ; but while the former, in order to account for the circulation of the 

 blood in man, calculated the force with which the heart contracts to be equal 

 to not less than a hundred and eighty thousand pounds weight at every con- 

 traction, the latter could not estimate it at more than eight ounces. 



In like manner Borelli, in applying the same theory to the power with 

 which the human stomach triturates, or, as we now call it, digests its food, 

 calculated it, in conjunction with the assistance it receives from the auxiliary 

 muscles, which he conceived to divide the labour about equally with itself, 

 as equal to two hundred and sixty-one thousand one hundred and eighty-six 

 pounds; and, Pitcairn has made it very little less, since he estimates the 

 moiety contributed by the stomach alone at one hundred and seventeen thou- 

 sand and eighty-eight pounds ; which gives to these organs jointly a force 

 more than equal to that of twenty mill-stones ! " Had he," says Dr. Munro, 

 " assigned five ounces as the weight of the stomach, he had been nearer the 

 truth."* 



The fallacy of this theory, however, and especially as it applies to the sto- 

 mach, has been completely exposed in our own day, by the well-ascertained 

 fact, that though the muscular coat of the stomach in most animals bears 

 some part in the process of digestion, this important operation is almost en- 

 tirely performed by a powerful chemical solvent secreted by the stomach 

 itself for this very purpose, and hence denominated the gastric juice ; and 

 which answers all the purposes of the most violent muscular pressure we can 

 conceive, and with a curious simplicity of contrivance. 



The laws of physical force will certainly better apply to the action of the 

 heart and arteries than to that of the stomach, and in some measure assist us 



* Comp. Anat. pref. p. viii. note. 



