558 



THE RESPIRATORY EXCHANGE 



of the tissues is exceedingly small or even absent altogether. The 

 tissues are constantly producing carbon dioxide, and here the 

 pressure of the gas appears to be the highest in the body. If pure 

 air be injected into a ligatured portion of the intestine of a living 

 animal, and then after a short time the gas be removed and 

 analysed, the partial pressure of carbon dioxide will be found 

 to have risen from zero to 7- 7 per cent, of an atmosphere. This 

 was the result obtained by Strassburg, and it has been recently 

 confirmed by Boycott, ( 31 ) who found that if successive observa- 

 tions be made, the pressure of carbon dioxide soon reaches a level 



100 



10 ZO 3O 40 50 60 7O 8O 9O 1OO HO 12O 13O 14V 15C 



FIG. 32. Pressure of Oxygen in Dog's Blood at 38 with different 

 Pressures of Carbon Dioxide (Bohr). 



which is maintained, at any rate for some hours. The balance 

 appears to result from the continual production of the gas by the 

 tissues, for it is greater if the blood-vessels, which supply the 

 intestine, have been previously ligatured. Such a value for the 

 partial pressure of carbon dioxide in the tissues is supported by 

 the experiments made by Strassburg and by Ewald upon the partial 

 pressure of the gas in urine, bile, and various pathological exuda- 

 tions ; pressures varying from 7 to 12 per cent, of an atmosphere 

 were obtained. 



Other factors may come into play. It has already been men- 

 tioned that Bohr, Hasselbalch, and Krogh found that the pressure 

 of carbon dioxide alters the dissociation curve of oxy-haemoglobin ; 

 this would have an important influence upon the transference of 



