88 



METABOLISM AND NUTRITION 



being led off to suitable apparatus for the absorption of carbon dioxide and 

 water. 



[A smaller apparatus embodying the same principles has been constructed 

 by Voit for experiments on smaller animals (Fig. 41). The cage (A) is ven- 

 tilated by a current of air kept moving by rotation of the gas meter (D). 

 Throughout the experiment a sample of this air is continually led off by a side 

 tube (E) and is passed over pumice stone soaked in sulphuric acid and then 

 through Ba(OH) 2 . The quantity of H 2 O in this air is obtained directly by the 

 difference in the weight of the H,SO 4 flasks, 1 the amount of CO 2 by titration 

 of the Ba(OH) 2 . The large gas meter (D) measures the total volume of air 

 passing through its works, and the small gas meter (H) measures the volume 

 of the sample. A duplicate analysis is made by means of a second set of 



FIG. 42. The respiration apparatus of Sondn and Tigerstedt. A, container for sample of the 

 room air; B, apparatus for determination of CO2; C, electric motor; D, rheostat; E, hydraulic 

 pump. 



vessels, and this sample is measured by a similar gas meter. Duplicate analyses 

 of the air which enters the cage are made in the same manner and the respiratory 

 products calculated by difference. 



If the determination of water vapor is satisfactory, the amount of oxygen ab- 

 sorbed by the animal can be obtained by subtracting the combined weight of the 

 animal at the beginning of the experiment and the total ingesta for the period 



1 Voit and Pettenkoffer made very thorough tests of this method, and found that the 

 water is obtained to within 1 or 2 per cent, the slight error being due to condensation on 

 the walls of the tubes. Rubner, employing the same principles of ventilation for his calo- 

 rimeter, obtained still more exact results. By shortening the distance which the air must 

 travel on its way from the cage to the H 2 SO 4 flasks, he was able to prevent entirely the 

 condensation of water on the walls of the tubes. For short experiments he relied upon hair 

 hydrometers placed inside the cage. ED. 



