ADVANCED DEMONSTRATIONS 



397 



dilator fibres to the limbs have been recently demonstrated by Bayliss 

 in the posterior roots. Excitation, mechanical or electrical, of the 

 5th-7th lumbar and 1st sacral posterior roots causes prolonged vascular 

 dilatation of the hind limbs after a latent period of 2-8 sec. 



CHAPTER XLII. 

 THE CHEMISTRY OF RESPIRATION. 



Experiments to Demonstrate that the Blood Gases are Chemically 

 Combined in the Blood. Ten c.c. of defibrinated ox blood are placed 

 in a stout flask fitted with a rubber cork. A tube passing through 

 the cork is connected with a 

 Geryk air-pump. The flask 

 is immersed in broken ice. 

 On making a vacuum there 

 occurs no perceptible evolu- 

 tion of gas until the flask is 

 removed to a bath of warm 

 water. The blood then sud- 

 denly bubbles and froths and 

 the gases come off. Note 

 the change of colour in the 

 blood when this happens. 

 If the thin film on the side 

 of the flask be examined 

 with the spectroscope, it will 

 give the band of reduced 

 haemoglobin. Further proofs 

 of the chemical combination 

 of 2 are these : O 2 can be 

 displaced by an equal volume 



nf f!O O in IfllrpH Klnnrl ic 



i uu , U 2 ir 



displaced by ferricyanide of 

 potassium with the reduction of the latter to ferrocyanide, and the 

 formation of methaemoglobin. 



The co-efficient of absorption of blood for oxygen is a little less than 

 water, i.e. 1 vol. absorbs -02616 at 30 C. when exposed to an atmosphere 

 of oxygen. Less than vol. % 2 can therefore be simply absorbed 

 by the blood at body temperature. The amount of oxygen in serum 

 is only 0'26 per cent. ; 1 grm. of pure crystalline haemoglobin absorbs 

 1-25 c.c. 2 (Haldane). There is about 14 per cent of haemoglobin in 



PI 



257. Geryk air-pump. The piston is covered with 



* rin valve ur . ng . tg agcent> 



