CONTRACTILITY. 27 



Emily. What a bright and beautiful red these mus- 

 cles present ; pray what is the cause of this brilliant hue ? 



Dr. B. It is probably owing to a portion of blood 

 still remaining in their vessels, or effused between their 

 fibres. Whatever it may be, it does not seem essential, 

 for by maceration in hot water or alcohol, they may be 

 deprived of it without altering their texture in the least. 

 The muscles of fishes are perfectly white, and so are 

 some of those in man which are not in the form of large, 

 fleshy masses. 



Emily. Are the properties of the muscular tissue as 

 simple and common as those of the cellular ? It is so 

 different in appearance, that I am expecting to find that 

 its properties are very different from, if not more com- 

 plex, than those of the latter. 



Dr. B. Your conclusion is correct. Muscle, as it 

 exists in the body in connexion with the cellular tissue 

 possesses both physical and vital properties. The first 

 of these it owes to the cellular tissue, and of course are 

 the same as those we have already described ; but its 

 peculiar and specific property, is strictly of a vital na- 

 ture. It is called contractility. By virtue of this pro- 

 perty the muscular tissue possesses the power of short- 

 ening itself on tha application of various kinds of stim- 

 ulants. Let a fibre be exposed and pricked with a 

 needle or wet with a drop of aqua- fords, and you will 

 see its two extremities approaching each other by re- 

 tracting, and the middle becoming swollen and hard. 

 This property of contractility is the source of immense 

 power 5 it is by muscular contraction that the various 

 movements of the body are effected, as well as some of 

 the most important actions of life. 



Emily. To tell the truth, Dr. B., I do not see very 

 clearly how it differs from elasticity. The fibre it ap- 

 pears, yields to the force which is applied, and returns 

 to its original condition when that cause is removed. 

 Is there any thing more in this than what we witness in 

 elasticity ? 



