THE NERVOUS MECHANISM OF RESPIRATORY MOVEMENT 313 



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

 carbon dioxide passing through the chamber, and the total quantity for 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 of Stimulating Cutaneous Nerves. Use a small dog or a 

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



FIG. 2466. 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. 



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 

 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. 



Now stimulate the skin of the abdominal region, the groin, with a com- 

 paratively strong induction current, figure 2466. Dissect out the sciatic 

 nerve, cut it, stimulate the central end with a mild to medium strength of 



