96 SPECIAL PHYSIOLOGY 



of the nerves. Fill the cell; join up with contact key in the primary 

 circuit, and a short-circuiting key in the secondary circuit. Test 

 the apparatus to see if everything is in order. Group "d" should 

 keep all the records of pulse or other observations. 



3. Operation. Group "a." (1) Pour 1 c.c. or 2 c.c. of sulphuric 

 ether upon the cotton in the cone; place the cone over the rabbit's 

 nose; observe and note carefully the three stages of anaesthesia. 



(2) Carefully note the rate of the heart before beginning anaes- 

 thesia, and the influence of anaesthesia upon rate and strength of 

 heart and respiration. 



(3) Keep the cotton moist with ether; watch the respiration and 

 pulse, and be careful not to give the animal too much and thus 

 interrupt the experiment. 



Group "b." Wash the clipped surface of the throat. After the 

 rabbit is completely anaesthetized, make with scissors a median 

 incision through the skin, beginning at the anterior end of the sternum 

 and cutting anteriorly for about 5 or 6 cm. ; divide the subcutaneous 

 connective tissue over the middle of the trachea. Carefully separate 

 from the median line on either side laterally the subcutaneous con- 

 nective tissue with the associated adipose tissue. 



How many pairs of muscles come to view? What two muscles 

 approach the median line to form the apex of a triangle at the anterior 

 end of the sternum? Observe a pair of thin muscles lying dorsal 

 to the muscles just mentioned, and joining them in the median line 

 to form a thin muscle sheet covering the trachea on its ventral side. 

 What muscles are these? 



Carefully lift up the median edge of the sternomastoid muscle 

 and separate with the handle of a scalpel or a seeker the delicate 

 intermuscular connective tissue. A bloodvessel and several nerves 

 come into view. 



Is the bloodvessel an artery or a vein ? . How many large nerves 

 accompany the bloodvessel? 



Take hold of the sheath of the vessel; lift it up and note in the 

 connective tissue accompanying the bloodvessels two nerves, one 

 large and one small. When the artery is in its normal position, 

 what relation do these two nerves sustain to it ? Which of the two 

 nerves is external and which is dorsal to the bloodvessel? Which 

 is in close relationship with the artery? The larger of the two 

 nerves is the vagus or pneumogastric. 



In preparing the nerve for stimulation one should neither grasp 

 it with the forceps nor with the fingers. It may be separated from 

 the delicate connective tissue in which it lies by use of a blunt seeker. 

 Far better than any metallic instrument is a small glass rod drawn 

 to a point, curved and rounded in the Bunsen lamp. Prevent the 

 tissues drying up by occasionally pressing them lightly with pledgets 

 of cotton moistened with normal salt solution. Adjust the electrode 



