RESPIRATION 63 



cc. of oxygen per 100 cc. of blood) , and introduced other improve- 

 ments. 6 



In the presence of free oxygen haemoglobin is a very unstable 

 substance, and soon decomposes, owing to the action of bacteria, 

 etc. ; but in the absence of oxygen the color of haemoglobin is per- 

 fectly stable, and this is also the case for carboxyhaemoglobin. The 

 standard solution was therefore saturated with carbon monoxide 

 in the absence of oxygen, and in this form is permanent. The blood 

 under examination is also saturated with carbon monoxide by 

 contact with coal gas or a little carbon monoxide. The two solu- 

 tions are thus spectrally the same. With these improvements the 

 Gowers haemoglobinometer became an extremely accurate instru- 

 ment for ascertaining the oxygen capacity of blood, and the ac- 

 curacy of any particular instrument could be controlled at once 

 by the ferricyanide method. Certain ever-recurring criticisms of 

 the instrument are almost entirely based on want of acquaintance 

 with the physiological principles of colorimetric methods, or of 

 the chemical facts on which the method is based. A detailed de- 

 scription of the method will be found in the Appendix. 



The percentage oxygen capacity (or haemoglobin percentage) 

 in the blood varies quite appreciably from hour to hour and day 

 to day, according as the total volume of the blood varies from ad- 

 dition or withdrawal of liquid. There are also variations associ- 

 ated with age and sex ; and pathological variations may be very 

 marked and significant. As regards age and sex I found the follow- 

 ing average relative figures for the percentage oxygen capacity 

 of the blood. 



Men 18.5 



Women 16.5 



Children 16.1 



It has been known for long that when an oxyhaemoglobin 

 solution is overheated or treated with various simple reagents the 

 oxyhaemoglobin decomposes into a coagulated protein and a 

 deeply-colored brown substance soluble in alcohol and certain 

 other solvents, and known as haematin. The haematin contains 8.7 

 per cent of iron, and the coagulated protein is free from iron. To 

 the haematin the formula C3 4 H 34 N 6 O 5 Fe has been assigned. By 

 the action of reducing agents the haematin loses oxygen and 

 changes to a purple color, with a corresponding change of spec- 

 trum, described by Stokes at the same time as he described the 



8 Haldane, Journ. of Physiol., XXVI, p. 497. 



