RESPIRATION 127 



in the groove of a shielded electrode. Stimulate gently. If you have 

 dissected out only the phrenic and posterior to its three tributaries, 

 the stimulation will be followed by a tetanic contraction of the 

 corresponding side of the diaphragm. If, however, one has taken 

 up with the phrenic a communicating thread, passing from one root 

 of the brachial plexus to another, the stimulation will be followed 

 by a tetanic contraction, not only of the diaphragm, but also of some 

 of the muscles of the front leg of the side operated upon. As this 

 will disturb the result the error must be corrected. The nearer the 

 clavicle one can get the nerve the more unlikely he is to get nerve 

 fibres belonging to the brachial plexus. 



4. Observations, (a) Tactile Observation of the Diaphragm. (1) In 

 what condition is the diaphragm during inspiration? Expiration? 



(2) In what position is the diaphragm during these two phases 

 of respiration? 



(3) What parts of the diaphragm make the greatest change of 

 position during inspiration? 



(4) What causes the diaphragm to arch anteriorly during normal 

 expiration? Are the conditions changed during the present observa- 

 tions? 



(5) Are the diaphragmatic movements synchronous with the costal 

 movements ? 



(6) The Normal Phrenogram. (6) Take a phrenogram. What may 

 be learned from it? 



(7) Without varying the adjustment of the phrenograph take 

 a tracing while repeatedly interrupting the respiration by hold- 

 ing the nostrils. What does the phrenogram show? What is the 

 interpretation ? 



What effect upon intrathoracic pressure would holding the nostrils 

 have? 



(c) The Phrenic Nerve and its Function. (8) Describe minutely the 

 relations of the nervus phrenicus in the neck. 



(9) Cut the nerve while tracing a phrenogram from the left side 

 of the diaphragm. Note the result. 



(10) Take a phrenogram from the right side of the diaphragm. 

 Does it differ essentially from the normal? 



(11) While taking the left phrenogram stimulate the distal end of 

 the left phrenic nerve. Interpret the result. 



(12) While taking a right phrenogram stimulate the distal end of 

 the left phrenic nerve. Interpret the result. 



(13) Dissect out and cut the right phrenic nerve. Does the 

 diaphragm cease to move? If it moves, is its movement active or 

 passive? Does it move backward during inspiration and forward 

 during expiration? If so, what causes it to make these movements? 

 If the movements are reversed, what has caused the change? 



Account for the phenomena. Kill the animal with chloroform. 



