272 A MANUAL OF PHYSIOLOGY 



or ACE mixture. Insert a cannula into the trachea (p. 177), and 

 connect it with the large bottle by a tube. Connect the bottle with 

 a recording tambour adjusted to write on a drum, and regu'ate the 

 amount of the excursion of the lever by slackening or tightening the 

 screw-clamp. Set the drum off at slow speed, and take a tracing. 



(^) Then disconnect the cannula from its tube. Dissect out the 

 vagus in the lower part of the neck, pass a ligature under it, but do 

 not tie it. Connect the cannula again with the bottle, and while a 

 tracing is being taken ligature the vagus. Then stimulate its central 

 end with weak shocks, marking the time of stimulation on the drum. 

 Repeat the stimulation with strong shocks, and observe the results. 



(c) Apply a strong solution of potassium chloride with a camel's- 

 hair brush to the central end of the vagus while a tracing is being 

 taken, and observe the effect. 



(d) Isolate the sciatic nerve (p. 185), ligature it, and cut below the 

 ligature. Stimulate its central end while a tracing is being taken. 

 The respiratory movements will be increased. 



(e) Disconnect the cannula, and isolate the vagus on the other 

 side. While a tracing is being taken, divide it. The respiratory 

 movements will probably at once become deeper and less frequent. 



(/) Again disconnect the cannula. Isolate the superior laryngeal 

 branch of the vagus, which will be found coursing inwards to the 

 larynx at the level of the upper edge of the thyroid cartilage. Liga- 

 ture the nerve, and divide it between the larynx and the ligature. 

 Reconnect the cannula. Take a tracing first with weak and then 

 with strong stimulation of the central end of the superior laryngeal. 



(x, r ) Insert a cannula into the carotid artery. While a tracing is 

 being taken, allow the blood to flow. Dyspnoea and exaggeration of 

 the respiratory movements will be seen when a considerable quantity 

 of blood has been lost. Mark and varnish the tracings. In the 

 whole of this experiment the cannula is to be disconnected, except 

 when the lever is actually writing on the drum, in order that the 

 period during which the animal must breathe into the confined space 

 of the bottle may be diminished as much as possible. 



2. The Effect of Temperature on the Respiratory Centre Heat 

 Dyspnoea. Set up an arrangement for taking a respiratory tracing as 

 in i. Anaesthetize a dog, and fasten it, back downward, on a holder. 

 Make an incision in tlie middle line of the neck, commencing a 

 little below the cricoid cartilage, and extending down for 4 or 5 

 inches. Insert a cannula into the trachea. Isolate both carotid 

 arteries for as great a distance as possible, and arrange them on the 

 brass tubes shown in Fig. ioo. Connect two adjacent ends of the 

 tubes by a short rubber tube. Connect one of the remaining ends 

 to a funnel, supported on a stand, and the other to a rubber tube 

 hanging over the table above a large jar. Slip two or three folds of 

 paper between the tubes and the vagus nerves. Heat two or three litres 

 of water to 55 or 60 C. Now connect the tracheal cannula with 

 the bottle. As soon as the tracing is under way, let the hot water 

 run through the funnel and tubes into the jar. Mark on the tracing 

 the point at which the flow of the hot water was begun, and go on 



