ANIMAL MECHANISM. 



63 



characteristics of the action of a muscle according to the 

 impulse of its volume or its length. And as a theory is 

 always required to satisfy the mind, this author sought to 

 interpret these different effects by a theory of the structure of 

 the muscles. 



Let us imagine, said he, a minute chain of metal formed 

 of circular elastic rings, and that an extensile force should be 

 exerted on this chain. Each ring will change its shape and 

 assume an oval form, and the whole chain will be lengthened 

 in proportion to the number of its rings. When it recovers 

 itself, under the influence of elasticity, the chain will grow 

 shorter again in proportion to its length. The minute chain 

 of Borelli is the primitive fibre revealed to us in the animal 

 economy by the microscope. But, said Borelli, if we form a 

 bundle of a great number of these chains, each one of them 

 will resist the extensile force in proportion to the elasticity of 

 its rings, that is to say, the thickness of the bundles, and the 

 force with which the extended bundle will recover itself will 

 be in the same ratio. 



We do not reason otherwise now that histology has shown 

 us, in a muscle, a bundle of fibres whose actions are com- 

 bined like the chains suggested by the Naples professor. 



Passing to other considerations, this author studied the 

 influence exerted by the direction of the fibres on the force 

 which they develop. He remarked that the muscles whose 

 fibres converge obliquely on the same tendon, like the barbs 

 of a feather on the central shaft, afford neither a range nor 

 an effort proportionate to their length and their sections. We 

 have no modification to make of this estimate of the composi- 

 tion of forces in the muscular organ. 



Of the specific force of muscles. — In the machines constructed 

 by man, it is not enough to measure the longitudinal and 

 transverse dimensions of the cylinder, in order to know what 

 quantity of work each stroke of the piston will develop ; we 

 must also know under what pressure the steam acts. That 

 is estimated by the number of atmospheres it can lift as it 

 escapes. At other times the force of the steam is measured 

 by the number of kilogrammes of pressure which it exerts on 

 every square centimetre of the surface of the cylinder. In 



