OP THE ORGANISM. 97 



is called tonicity; in the vessels where it is more marked, it is 

 called vascular contractility, and in the muscles where it is 

 greatest, muscular irritability or myotility. 



It is remarkable that all these movements consist in contrac- 

 tions. It has been thought, however, that certain movements 

 depended upon an expansion, an elongation, or a turgescence,* 

 this appears to have been caused by a want of close observa- 

 tion. 



102. In man, and in those animals that have distinct nerves 

 and a nervous centre, the impressions received are transmitted 

 by the nerves, and felt at the centre, and the centres transmit 

 their action to the muscles by the nerves. The cause to which 

 these phenomena are attributed, is called the nervous force, in 

 one word, sensibility. Among the sensations, some are ex- 

 tremely obscure, and but vaguely perceived, t They are pretty 

 nearly every where extended, particularly in the mucous mem- 

 branes. In a state of health, they constitute a general senti- 

 ment of well being; when they are increased by certain causes, 

 they give rise to a morbid sensation called pain. There is no 

 part which may not become the seat of this morbid sensibility. 

 The other sensations are distinct, and some of them altogether 

 special. 



As to the nervous action on the muscles, it directs their ir- 

 ritability; its power is also extended to the vessels, particularly 

 to the smallest. 



Moral and intellectual acts, differ so widely from organic 

 phenomena, that it is impossible they can depend on the same 

 cause; they would in this case be necessary and blind, instead 

 of being enlightened and free. Physiology, which on the one 

 side is met by natural philosophy, here encounters moral phi- 

 losophy or metaphysics. 



103. The functions are not exercised, or if you will, the 

 vital forces do not enter into action spontaneously, but by 

 means of stimulants or exciting causes; whether they be the 

 bodies which act on the external and internal surfaces of the 

 body, or the blood which penetrates all its parts. In relation 



* See Hebenstreit, Jf Turgore v'ltati. Lipsix, 1795. 

 f See Hubner, de Coenxsthesi/ Hal*. 1794. 



