292 The Older Doctrines [lect. 



a stimulus, such as pricking, or pinching, or some chemical 

 substance be applied. 



Many writers consider this living contractile force as iden- 

 tical with the dead one just described as belonging more or less 

 to all tissues. This view Haller discusses and concludes, " that 

 " muscular fibre is the only one which is moved spontaneously 

 "in the living animal, or is brought by irritaments from rest to 

 "movement," and that "the living contractile force must be 

 " held to be distinct from the dead contractile force, since the 

 "two agree neither in the laws which govern them, nor in 

 "their duration, nor in their seat." 



This force he calls the vis insita, the ' inherent force,' and 

 the tissues possessing it he calls after Glisson ' irritable.' 



He then discusses whether this property of irritability is 

 identical with that of feeling, and concludes that it is not. 

 " There are many parts which feel but which are not irritable, 

 " and in particular a nerve, which is above everything sensitive, 

 " and yet possesses no contractile force except that common one 

 " found as stated above even in dead things. 



" Wherefore this force since it is different both from mere 

 " elasticity and from that dead contraction which is common to 

 " all fibres, seems to constitute a peculiar property, proper to 

 " the muscular fibre, and indeed to mark the character of that 

 " fibre, so that every muscular fibre is irritable, and on the 

 " other hand you may fairly call muscular fibre everything that 

 " is irritable. It is however a force of its own kind, different 

 " from every other power, and to be classed among the sources 

 " of the production of motion the ultimate cause of which is 

 " unknown. This same force is inherent in the fibre itself and 

 " not brought to it from without." 



He sums up thus : 



"I (by my experiments published first in 1739, and again 

 "in 1743) separated this irritable nature on the one hand from 

 "a mere dead force, and on the other from the nervous force 

 " and from the power of the soul. I shewed that the move- 

 " ment of the heart and the irritable nature of the intestines 

 " depended on it alone. I confined it entirely to the muscular 

 " fibre, in which point the Batavian school does not agree with 



