32 LECTURE I. 



nected with matter of different qualities 

 and arrangements. The flesh of animals 

 and that of fish are different in quality ; 

 the pulpy medusae which float in the sea 

 differ from vegetables ; yet all are irritable, 

 or possess this power of occasional con- 

 traction. Though in general we find irri- 

 tability connected with a fibrous structure, 

 yet, if we may trust our senses, it is not so 

 in every instance. In the hydatid, where 

 no such structure is apparent even with 

 the aid of lenses, we still have evidence 

 of the irritability of life. If also, as I 

 strongly suspect, the muscular fibres be not 

 continued from one end of the muscle to 

 the other, irritability could not in that case 

 be considered as a property belonging to 

 them, since any breach of continuity would 

 completely frustrate the contraction of the 

 whole muscle. 



Thirdly, I proceed to enquire into Mr. 

 Hunter's opinion, that irritability is the 

 effect of some subtile, mobile, invisible sub- 

 stance, superadded to the evident structure 

 of muscles, or other forms of vegetable and 



15 



