IIo A CHEMICAL SIGN OF LIFE 
3.0 parts of carbon dioxide present in 10,000. The 
delicacy of the apparatus can be illustrated by the kind 
of experiments we can use it for, e.g.: 
1. The different rates at which carbon dioxide is pro- 
duced by a single fertilized and a single unfertilized egg 
of a fish (Fundulus hectroclitus) can be distinguished. 
2. The unequal rate of metabolism of two different 
species of the little banana flies can be detected within 
ten minutes by using a single insect in each chamber. 
3. The vitality of a single kernel of wheat can be 
detected in ten minutes. 
4. The daily variation of respiratory activity of a 
single isopod has been determined. 
5. The carbon dioxide production of the different 
parts of a small nerve fiber can be measured, and the 
unequal rates of different segments of the nerve detected. 
6. The effect on the metabolic rate of the muscular 
contractions of very small animals, like a worm or insect, 
or the effect of light on small pieces of a leaf, can be 
demonstrated in the class in a few minutes. 
7. By the use of proper reagents small quantities of 
many other gases can be measured. 
Principle of the method.—The principle of the method 
was first devised in conjunction with Dr. H. N. McCoy, 
and, with some modifications, the biorneter is constructed 
so as to conform thereto. The principles involved are as 
follows: 
1. Exceedingly minute quantities of carbon dioxide 
can be precipitated as barium carbonate on the surface 
of a small drop of barium hydroxide solution. 
2. When the drop of barium hydroxide is exposed to 
any sample of a gas free from carbon dioxide it remains 
