288 RESPIRATION 



c. The percentage of carbon dioxide in the air which leaves the chamber. 



If the animal is small enough, for example, the guinea-pig or a mouse, 

 the absorption tubes may be constructed of proper size to absorb all the 

 carbon dioxide passing through the chamber, and the total quantity of any 

 unit of time determined directly in grams. If now the animal is weighed 

 at the moment it is introduced into the cage, then the amount of carbon 

 dioxide per kilo weight can be quickly computed. 



Calorimeters for larger animals require a larger volume of ventilation, 

 and the usual procedure is to measure the percentage in a sample as directed 

 above. 



ii. The Nervous Mechanism of Respiratory Movement. 



a. The Effect oj Stimulating Cutaneous Nerves. Use a small dog or a 

 cat for this experiment; anesthetize and introduce a tracheal tube with a 

 side branch adapted for measuring the variations of pressure during respira- 

 tion. Connect the free limb of the tracheal tube with an ether apparatus 

 and adjust to secure constant anesthesia. Connect the side branch of the 



on 



FIG. 246. ^Change in Respiration on Stimulating the Central End of the Sciatic Nerve. The 

 rate is sharply increased and the amplitude more than doubled. The stimulation is between the 

 points marked on and off, time in seconds. The inspiratory movement following the stimulation 

 was greater than the limit of the recording tambour. 



tracheal tube with a Marey's recording tambour of medium size and supply 

 with a comparatively delicate membrane. The amplitude of the move- 

 ments of the tambour may be regulated by a screw compress on a connecting 

 tube. Arrange an induction coil with platinum electrodes in the usual 

 manner, figure 318, for stimulating, by means of the interrupted current. 

 Record the results of the experiment along with the variations of blood pres- 

 sure on a continuous-paper kymograph; the instrument should be supplied 

 with a time signal, a stimulating signal, etc. 



