no 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 biometer 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 



