RESPIRATORY INTERCHANGE, CALORIMETRY 315 



ments, an extension of the limbs, and gasping movements of the mouth, after 

 which the animal remains quiet, death being produced by asphyxia. 



13. Respiratory Interchange, Calorimetry. The experiments are 

 conducted in such a manner that comparative analyses may be made 

 between the air inspired and that expired. Generally an animal is placed 

 in a chamber, called the respiratory chamber, which is then closed except 

 for two openings, one for the entrance of the inspired air, the other for the 

 escape of expired air. Some form of pump is used for renewing the air in the 

 chamber. Both the inspired and expired air is made to pass through reagents 

 which w r ill absorb the contained carbon dioxide, such as baryta water or soda- 

 lime, and in turn through reagents which will absorb the watery vapor. When 

 the experiment is completed the differences between the two are determined. 

 The difference in oxygen has to be calculated, and is open to error. The 

 famous respiratory chamber of Pettenkofer is large enough to perform such 

 experiments on man, and is of very elaborate construction. But the most 

 perfect apparatus assembled for this purpose is the respiration calorimeter of 

 Atwater constructed for man, and the respiration apparatus of Armsby for 

 cattle. 



