94 A CHEMICAL SIGN OF LIFE 
air free from carbon dioxide, and a drop of barium 
hydroxide is introduced at the top of the tube in each 
chamber. If the crushed seed gives off more carbon 
dioxide than the uncrushed, as evidenced by a larger 
deposit of the carbonate on the top of the drop in the 
chamber containing the crushed seed, the seed is alive. 
If the seeds are alive, such a distinction in the carbon 
dioxide output will be noticeable in a few minutes in 
some cases, or in an hour or more in other cases, .all 
depending on the size, the number, and the kind of seed 
we are testing. With several seeds, as with the fresh 
nerve of a frog, we can detect vitality in this way in a 
few minutes. 
