180 PRACTICAL PHYSIOLOGY 



The Graphic Record of the Respiratory Movements. For this 

 purpose an instrument known as the stethograph is used. There are 

 various forms, two of which are shown in Figs. 177 and 178. A 

 receiving tambour constructed like a drum is fastened to the chest, and 

 is connected with a recording tambour, the lever of which writes on a 

 smoked drum The subject of the experiment should not be allowed 

 to see the movements of the lever, for the respiration is easily affected 

 by nervous impressions. Take a graphic record of the respirations and 

 mark the time relations of inspiration and expiration by means of a 

 chronograph giving seconds. 



CHAPTER XLVI. 

 CHEMISTRY OF RESPIRATION. 



The Composition of Inspired Air, Expired Air and Alveolar Air. 

 For the analysis of these different samples of air the best apparatus 

 is that of Haldane. The gas is measured in the graduated gas-burette 



A, provided with a three way tap. Surrounding the /gas-burette is a 

 water-jacket. The whole is supported by a clamp and retort stand. 

 The gas-burette is connected by pressure tubing to the levelling tube 



B, which is held by a spring clamp attached to the retort stand. A 

 and B contain mercury, and by raising or lowering B gas can be expelled 

 from or drawn into A. One of the connections of the three-way tap is 

 used for taking in the sample, the other connects the burette with 

 an absorption apparatus arranged as in the figure. 



The bulb E, filled with 20 per cent, caustic potash, absorbs carbon 

 dioxide. The bulb F, filled with alkaline pyrogallic acid solution, 1 

 absorbs oxygen. The water in Gr and H protects the pyro. solution 

 from the air. F can be emptied and refilled through K when it is 

 necessary. The tap on the absorption pipette places either E or F 

 in connection with the gas burette. 



The pressure in the burette is adjusted by using the potash pipette 

 as a pressure gauge and bringing the potash before every reading of 

 the burette to the mark M. In order to make the reading of the 

 burette independent of changes in temperature and barometric pressure 

 during analysis a control tube N is employed. N is connected with 

 the potash solution by means of a 1-tube. The tap at P makes it 



1 Dissolve 100 grms. of stick caustic potash in 50 c.c. of water. Add 10 grins, 

 of pyrogallic acid to this solution. 



