84 OF THE MUSCLES. 



ments for the service, and how many such contribute their 

 assistance to the effect. Breathing with ease is a blessing 

 of every moment ; yet, of all others, it is that which we 

 possess with the least consciousness. A man in an asthma 

 is the only man who knows how to estimate it. 



IV. Mr. Home has observed,* that the most important 

 and the most delicate actions are performed in the body 

 by the smallest muscles; and he mentions, as his examples, 

 the muscles which have been discovered in the iris of the 

 eye and the drum of the ear. The tenuity of these mus- 

 cles is astonishing. They are microscopic hairs ; must 

 be magnified to be visible ; yet are they real effective mus- 

 cles ; and not only such, but the grandest and most pre- 

 cious of our faculties, sight and hearing, depend upon their 

 health and action. 



V. The muscles act in the limbs with what is called a 

 mechanical disadvantage. The muscle at the shoulder, by 

 which the arm is raised, is fixed nearly in the same manner, 

 as the load is fixed upon a steelyard, within a few decimals, 

 we will say, of an inch, from the centre upon which the 

 steelyard turns. In this situation, we find that a very heavy 

 draught is no more than sufficient to countervail the force 

 of a small lead plummet, placed upon the long arm of the 

 steelyard, at the distance of perhaps iifteen or twenty inches 

 from the centre, and on the other side of it. And this is 

 the disadvantage, which is meant. And an absolute dis- 

 advantage, no doubt, it would be, if the object were to 

 spare the force of muscular contraction. But observe how 

 conducive is this constitution to animal conveniency. Me- 

 chanism has always in view one or other of these two pur- 

 poses ; either to move a great weight slowly, and through 

 a small space ; or to move a light weight rapidly, through 

 a considerable sweep. For the former of these purposes, 

 a different species of lever, and a different collocation of 

 the muscles, might be better than the present ; but for the 

 second, the present structure is the true one.. Now, so it 

 happens, that the second, and not the first, is that which 

 the occasions of animal life principally call for. In what 

 concerns the human body, it is of much more consequence 

 to any man to be able to carry his hand to his head with 

 due expedition, than it would be to have the power of rais- 

 ing from the ground a heavier load (of two or three more 

 hundred weight, we will suppose,) than he can lift at pre- 



*Phil. Trans, part 1. 1800. p. 8. 



