36 ittiiMoiil OF BARON HALIER. 
homing vein, I could not have failed to have dis- 
covered it.” 
Next in order come those parts in which irrita- 
bility is unequivocally marked, and in which it 
appears to be naturally inherent. These are espe- 
cially the flesh of animals, the muscular fibre 
wherever it can be traced, w T hether in the external 
coverings or internal viscera. The different struc- 
tures, indeed, appear to be irritable in proportion as 
they are muscular ; and hence we are not surprised 
to find that the heart, which is nothing more than 
a set of great hollow muscles, is especially endowed 
with this property ; and that this is most remarkably 
true in regard to cold-blooded animals. In the eel, 
motion is conspicuous in the heart several hours 
after it has been removed from the body; in frogs, 
it is apparent from noon till almost midnight ; and in 
some other animals, it continues as long as twenty- 
four and thirty hours after death. Even after it has 
ceased to move spontaneously, its irritability again 
manifests itself on the application of a slight stimu- 
lus. On the whole, it appears that no part of the 
animal frame is irritable independent of the muscular 
fibre, and that the property is peculiar to this fibre ; 
this remark, however, must not be extended to the 
insect world, which appears to have the singular 
quality of being both irritable and sensible all over. 
This property, which Haller denominated the vis 
insita, is distinct from all other known properties 
of bodies. Elasticity most nearly resembles it, but 
differs as it is peculiar to hard bodies, whilst irrita- 
