PHYSIOLOGY. 95 



" I now proceed to seek for the causes of the different states 

 of vigour : it may depend 



1. Upon the state of the simple solid (XIV. XXIV.). In 

 animals of different sexes, and of different temperaments, the 

 energy of the brain being given, the vigour of the body is cor- 

 respondent, in some measure, to the density and rigidity of the 

 simple solid. 



" 2. The bulk of the muscle. It is very generally observed, 

 that cceteris paribus, the larger animals are stronger than the 

 smaller; it has been supposed indeed it is probable that 

 the number of fibres is the same in the muscles of each ; there- 

 fore, if we admit that supposition of the equality of the fibres, 

 we shall find no particular advantage from the length, so that 

 there must be somewhat in the manner in which the fibres are 

 collected into the belly of the muscle that promotes the vigour 

 of the whole. In men of the same stature the strength is ma- 

 nifestly as the bulk of the muscles ; the painters know this very 

 well, when they express their Hercules by the swelling they give 

 to the several muscles ; and nothing serves to prove this better, 

 than that when exercise gives an increase of strength, it, at the 

 same time, always gives an increase of bulk in the muscles. 

 We had many years ago in this country a very strong man of 

 the name of Topham ; his feats of strength were mostly per- 

 formed by his arms, and his legs were little employed. I, along 

 with several anatomists, examined him ; and we found that while 

 his legs were soft, and rather resembled those of a woman, the 

 bulk of every muscle in the arm was very remarkable and con- 

 siderable. 



" 3. The state of the tension of the muscular fibre. If we 

 employ the analogy of the simple solid, we have sufficiently ex- 

 plained how far the tension gives a stronger degree of contrac- 

 tion ; and the excitement being given, I would explain it in the 

 muscular fibre in the same manner. But there is truly some- 

 what more here, for we know that this tension is capable even 

 of exciting a contraction, while the extending power continues 

 to be applied; we conclude, therefore, that tension actually 

 increases the excitement for the time, and so strengthens the 

 muscular fibres more in proportion than it does the simple solid. 

 A circumstance which particularly deserves to be taken notice 



