202 INTRODUCTION TO GENERAL PHYSIOLOGY 



blood by washing the corpuscles with 0.9 per cent, sodium chloride. 

 Centrifuge some defibrinated blood. Pour off the serum. Shake 

 up the deposit with saline and centrifuge again. After repetition 

 for two or three times there will be practically no serum left. The 

 reason for this procedure is that the sodium bicarbonate in the serum 

 gives off carbon dioxide to a vacuum, although it does not to the 

 tension of this gas in the air-cells of the lungs. 



The final suspension of corpuscles in saline is first put in the 

 pump and the gas removed. Then the process to which blood 

 was subjected in the former experiment is repeated, except that 

 the corpuscles are subjected to an atmosphere of carbon dioxide 

 in the bottle instead of to air. It will be found that much more 

 carbon dioxide is obtained in the pump afterwards than could be 

 dissolved in the water present. 



The carbon dioxide may be made in a Kipp generator, and 

 should be passed through sodium bicarbonate solution in order to 

 stop spray containing hydrochloric acid. 



Stimulation of Respiration by Carbon Dioxide 



Breathe from a football bladder a gas mixture containing about 

 10 per cent, of carbon dioxide, together with more oxygen than 

 serves to make up that displaced by the carbon dioxide. The 

 respiration will be found to be quickened and deepened, while the 

 feeling of "want of breath," as after running upstairs, will be 

 experienced. It may be found that less carbon dioxide will give 

 the result better. 



The oxygen is most conveniently obtained from a cylinder of 

 the compressed gas, but it may be made by the usual process of 

 heating potassium chlorate with manganese dioxide. It should be 

 washed by passing through caustic soda. A sample of the mixture 

 as breathed should be analysed in the apparatus used for the green 

 plant experiment (p. 184). 



Oxidation 



Autoxidation. Expose some benzaldehyde and also linseed oil in 

 shallow dishes to the air. Note that crystals of benzoic acid appear 

 in the former, and that the latter becomes hardened as in varnish. 



No effect is to be seen with sugar or lactic acid exposed to the 

 air. That they are not oxidised to carbon dioxide and water can 

 be shown by leaving a small quantity in a large closed bottle for 

 some days and determining the carbon dioxide content of the gas 

 in the bottle by analysis. Or, more simply, insert a perforated 

 rubber stopper with two tubes, and draw air, freed from carbon 

 dioxide by first passing through a wash-bottle of caustic soda, 

 through the bottle and then through lime-water. 



