32 



the principle of life may in some instance* 

 be suddenly removed, or have its power 

 abolished, whilst in general it is lost by 

 degrees. 



The contraction of irritability take* 

 place in some animals in a very slow 

 and gradual manner, and their muscles in 

 general are incapable of sudden contrac- 

 tion. Yet though the action of their 

 muscles is very slow, it is very powerful 

 and very permanent. The American sloth, 

 supports its weight for a very long time 

 in one attitude by fixing its claws into 

 the branches of trees ; an act which would 

 speedily weary muscles of an ordinary 

 character. The muscles of the legs of 

 birds that roost, seem to have a si- 

 milar power of permanent contraction. 



Mr. Carlisle has lately demonstrated a 

 peculiar distribution of the arteries in the 



