36 MEMOIR OF BARON HALLER. 



bouring vein, I could not have failed to have 

 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, whether 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- 



