PHYSIOLOGY; 



OR, 



THE LIVING BODY 



GENERAL PHYSIOLOGY. 



VITAL PROPERTIES OF THE TISSUES. 



THE animal tissues, the microscopical structure, chemical composi- 

 tion, and physical properties of which have now been described, pos- 

 sess and manifest, during life, certain further and peculiar properties, 

 altogether different from those exhibited by inorganic substances, at 

 once distinguishing them from such bodies, and enabling them to per- 

 form certain important uses in the living animal body. Hence these 

 properties have been named vital properties. Of these vital proper- 

 ties two are special, i. e., are confined each to one elementary animal 

 tissue or substance respectively ; whilst a third vital property is gen- 

 eral, i. <?., is manifested by all the living tissues. The two former 

 properties are contractility and sensibility ; whilst the latter is known 

 under several names, of which we prefer, as a general term, that of 

 the formative or organizing property. 



Vital contractility is the power possessed by certain tissues of con- 

 tracting, or shortening themselves, in one direction. It is especially 

 manifested by the fibres of muscular tissue, and is most probably the 

 source of all intrinsic motion in the living body ; for it is possibly 

 even the cause of ciliary motion, and of all the movements in animal 

 protoplasm. It is sometimes named irritability, and, more definitely, 

 muscular irritability: by Haller it was distinguished as the vis insita, 

 or vis musculosa. 



Sensibility is the special property of the nervous tissues. If taken 

 to represent all the vital properties of nervous substance, in which 

 general sense it is here understood, sensibility is a more complex en- 

 dowment than the contractility of the muscular tissue. It might be 

 spoken of as the nervous irritability, but a common and more appro- 

 priate term for it is the "excitability" of the nervous tissues. This 

 peculiar vital property of nervous excitability is manifested both by 

 the nerve-fibres and the nerve-cells. In the former, it appears as 



