2 9 6 



RESPIRATION 



(h) Insert a cannula into the carotid artery. While a respiratory 

 tracing is being taken, allow blood to flow from the artery. 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 tracheal cannula is to be dis- 

 connected, 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. 

 Instead of the method described, the stethograph shown in Fig. 136 

 may be used to obtain respiratory tracings from animals, a broad canvas 

 band being put round the animal's chest. To each end of this band is 

 clamped with sufficient tension a strong thread (F), fastened to a small 

 metal disc on the inside of the 

 rubber dam closing the obliquely- 

 cut ends of the metal cylinder D. 

 The tube G is connected with a 

 tambour or with a bellows recorder 

 (Fig. 137). 



4. The Effect of Temperature on 

 the Respiratory Centre Heat Dysp- 

 noea. Set up an arrangement for 



Fig. 136. Stethograph (Crile). 



Fig. 137. Bellows Recorder. B, a 



lead tube connected with the 

 small bellows A, which consists of 

 a light wooden base and top, to 

 which is cemented very flexible 

 (organ key) leather, properly 

 creased for expansion and con- 

 traction; C, writing lever. 



taking a respiratory tracing as in 2 

 (footnote, p. 294). Anaesthetize a 

 dog, and fasten it, back downward, 

 on a holder. Make an incision in 

 the middle line of the neck, com- 

 mencing 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. 138. 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 about 65 C. (a) Now connect the tracheal cannula with the 

 tambour. 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 passing 

 it until it has produced an effect. Then stop the drum, and circulate 

 water at the ordinary temperature till the breathing is again normal. 

 Then, while a tracing is being taken, pass ice-cold water through the 

 tubes, and again notice the effect. 



