CARBON-MONOXIDE HEMOGLOBIN. 399 



proportion to its partial pressure on the surface, it would 

 turn out no oxygen; the quantity of dissolved gases held 

 by a liquid being dependent only on the partial pressure of 

 each individual gas on its surface, and unaffected by 

 that of all others. During the taking up of carbon 

 monoxide the blood changes color in a way that can be 

 recognized by a practiced eye; it becomes cherry red instead 

 of scarlet. This shows that some new chemical compound 

 has been formed in it; examination with the spectroscope 

 confirms this, and shows the color change to be due to the 

 formation of carbon-monoxide haemoglobin which has a 

 different color from oxyhaemoglobin. A dilute solution 

 of reduced haemoglobin absorbs all the rays of light in one 

 region about the green of the solar spectrum (see Physics), 

 and so produces there a dark band; a thin layer of the blood 

 of an asphyxiated animal does the same. Dilute solution 

 of oxyhaemoglobin absorbs the rays in two narrow regions 

 of the solar spectrum at the confines of the yellow 

 and green, and arterial blood does the same. Dilute 

 solution of carbon-monoxide haemoglobin, or blood which 

 has been exposed to this gas, also absorbs the light in two 

 narrow bands of the solar spectrum; but these are nearer 

 the blue end of the spectrum than the absorption bands 

 of oxyhaemoglobin. Pure blood serum saturated with oxy- 

 gen gas or with carbon monoxide does not specially absorb 

 any part of the spectrum; therefore the absorptions when 

 haemoglobin is present, must be due to chemical compounds, 

 of those gases with that body. 



Since carbon-monoxide-haemoglobin has a bright red color, 

 we find in the Bodies of persons poisoned by that gas, the 

 blood all through the Body cherry red; the tissues being 

 unable to take carbon monoxide from haemoglobin in the sys- 

 temic circulation. Hence the curious fact that, while death 

 is really due to asphyxia, the blood is almost the color of 

 arterial blood, instead of very dark purple, a? in ordinary 

 cases of death by suffocation. Experiments with, animals 

 show that in poisoning by carbon monoxide persistent ex- 

 posure of the blood to oxygen, by means of fj-tificial respi- 

 ration, will cause the poisonous gas to be slowly replaced 



