RESPIRATION 137 



system, stimulating the respiratory center to increased activity, these 

 reflex movements frequently assume a spasmodic character. 



Inspect the internal aspect of the chest wall, and note the shape 

 of the thoracic cavity. Identify the pulmonary blood-vessels. Trans- 

 illuminate the border of either lung, noting its alveolar structure. Iden- 

 tify portions of the visceral pleura below the apex of the heart. Note 

 its structural peculiarities. 



7. The Phrenic Nerves. Isolate both phrenic nerves above the 

 diaphragm and place them in loose ligatures. These nerves are easily 

 found, because they descend in close proximity to the heart, the right 

 selecting the highway of the inferior vena cava. Stimulate them 

 separately with single induction shocks of moderate strength. Observe 

 the resultant contraction of the corresponding half of the diaphragm 

 and note the effect of this contraction upon the position of the ab- 

 dominal organs. Kill the animal by an overdose of ether. 



Trace the course of each phrenic nerve to its origin in the cervical 

 portion of the spinal cord. 



8. Swim Test. Grasp the tracheal cannula with your left hand, 

 and separate the trachea and 'lungs, together with the heart and large 

 blood-vessels, from the neighboring parts. Place this mass in water, 

 observing that the buoyancy of the lungs is sufficient to carry con- 

 siderable additional weight. How would an atelectatic lung behave 

 under these circumstances? What use is made of these facts medico- 

 legally? 



9. The Excised Lung. Remove the metal cannula from the model, 

 illustrating the manner in which the lungs are expanded. Insert this 

 cannula in the trachea of the excised lungs, and suspend this preparation 

 in the bell-jar. Repeat the observations made previously with the 

 rubber pouch. 



Remove the lungs. Compress them in the palm of your hand. 

 Are you able thereby to expel all the air from them? Repeat the swim 

 test. Explain your inability to render them air free. 



