$46 THE RESPIRATORY EXCHANGE 



processes. Hiifner and Fredericq have contested the accuracy 

 of Bohr's experiments, and suggest that the irregularities in the 

 results are evidence of a want of equilibrium between the pressures 

 of the gases in the blood and in the haemataerometer. It is to be 

 noted that the respiratory quotients in Bohr's experiments vary 

 from O54 tol'Ol, owing, it may be, to imperfect and irregular ventila- 

 tion of the lungs. It is probable also that the leech-extract added to 

 the blood may alter the absorption of gases, and it is certain that 

 the operative procedure renders the animal's condition abnormal. 



Fredericq has made experiments with an aerotonometer con- 

 structed upon the same principles as Pfliiger's instrument ; the 

 arterial blood is prevented from coagulation by a previous injection 

 of peptone, and after passing through the apparatus flows back 

 through a vein to the animal's body. The results yielded a pressure 

 of 12 to 14 per cent, for the oxygen, and 2*7 to 2'4 per cent, of an 

 atmosphere for the carbon dioxide. When the dog breathed a 

 mixture of about 85 per cent, of oxygen, the pressure of the oxygen 

 in the arterial blood was raised to 60 per cent, of an atmosphere. 



So great is the want of agreement and the irregularity of the 

 results obtained by different observers with various forms of tono- 

 meter that the suspicion arises that there are sources of fallacy 

 in the methods. Appeal must, therefore, be made to other experi- 

 ments, especially to those which can be performed upon the living 

 animal without subjecting it to any serious operation. This 

 latter condition is fulfilled by Haldane's method, the principle 

 of which is as follows : " The subject of the experiment con- 

 tinues to breathe air containing an exactly known very small 

 percentage of carbonic oxide until a point is reached at which 

 the percentage saturation of his haemoglobin with carbonic oxide 

 becomes constant. Now the final saturation with carbonic oxide 

 of haemoglobin solution brought into contact with gas containing 

 carbonic oxide and oxygen depends on the relative tensions of 

 the carbonic oxide and oxygen in the liquid, so that if the tension 

 of carbonic oxide, and the final saturation of the hemoglobin 

 be known, the oxygen tension can be inferred. Hence if in the 

 living subject both the carbonic oxide tension in the blood leaving 

 the lungs, and the final saturation of the haemoglobin with carbonic 

 oxide, are known, the oxygen tension of the blood leaving the 

 lungs can be calculated. But the carbonic oxide tension of the 

 blood leaving the lungs will (after absorption has ceased) be that 



