SUGGESTIONS FOR LABORATORY WORK 619 



longer effective. The junctions of preganglionic and postganglionic 

 neurons of the vagus path are in the heart tissue itself (p. 194). 



Arterial Pressure. Disconnect the heart from the recording 

 lever. If the heart is beating feebly or very slowly bathe with 

 warm water. If no response take a freshly prepared turtle. Trace 

 one of the large arteries to a point at least one inch from the heart. 

 At this point separate the artery carefully from surrounding tissues 

 for another inch. Squeeze the artery shut at the cardiac end of 

 the prepared portion by means of a spring clip. Pass a stout 

 thread around the prepared artery. Fill with salt solution a 

 small L-shaped glass tube, 15 inches high. Hold the solution in 

 the tube by closing the long end. Make a transverse cut half- 

 way through the prepared artery, slip the short end of the glass 

 tube through this out into the artery and tie it in place by means 

 of the thread previously prepared. The tube may now be opened 

 and the clip removed from the artery. The height at which the 

 column of salt solution is maintained measures arterial pressure. 



THE RESPIRATORY SYSTEM 



Dissection of Air Passages and Lungs of Sheep. Note the large 

 trachea (windpipe) with open rings of cartilage in its wall. Ob- 

 serve carefully the surface of the lung. Note the cellular appear- 

 ance and the delicate texture. Note the subdivision of each lung 

 into lobes. 



Inflate the specimen. 



Dissection. In one lung, follow the trachea down the bronchus 

 to its smallest branches. 



Starting at the heart follow the pulmonary artery and vein to 

 their finest branches. Use a probe and scissors. 



On the other lung tear away the tissues so as to show the inter- 

 lacing of these vessels. Use the forceps to pick with. 



Miser oscopic Study. The final subdivisions of the bronchi, and 

 their terminations in infundibula and alveoli, are microscopic. 

 Observe in prepared and stained sections the relatively thick 

 walled bronchioles, and the extremely delicate walls of the air 

 cells (infundibula and alveoli). The capillaries which run in the 

 alveolar walls cannot be seen in ordinary microscopic sections. 



Breathing Movements in Man. The following observations may 



