THE BLOOD. 495 



ordinary temperature ; and if haemoglobin is dried at. 

 a temperature above 100, it becomes dirty-brown, and 

 decomposes, yielding a brown coloring-matter, two 

 protein compounds similar to fibrin and albumen, and 

 several acids (formic, butyric). 



Light that has passed through an aqueous solution 

 of haemoglobin, or through blood, yields a spectrum 

 which shows two very characteristic absorption bands, 

 lying in yellow and green (between Frauenhofer's lines 

 D and E). If the blood is saturated with carbonic 

 acid, or heated to 40-50 after the addition of a drop 

 of ammonia, or if mixed with a drop of ammonium 

 bisulphide, both of these bands disappear, and, instead 

 of them, there appears a single band (between the 

 lines C and D, nearer C.). The original bands reappear, 

 however, immediately if the blood, thus treated, is 

 shaken with atmospheric air. 



The most remarkable property of haemoglobin is 

 its capability of uniting with oxygen and other gases, 

 to form peculiar unstable compounds, which also crys- 

 tallize, and give up these gases very readily, even in a 

 vacuum, without losing the capability of reuniting 

 with the gases. Haemoglobin containing oxygen is 

 bright red, that which contains no oxygen is 

 darker. This is the cause of the different color of 

 arterial (with haemoglobin containing a great deal of 

 oxygen) and venous blood (with haemoglobin contain- 

 ing little or no oxygen) ; the optical phenomena above 

 mentioned also find their explanation in this fact. 

 Only the haemoglobin containing oxygen (oxyhaemo- 

 globin) gives the characteristic absorption-bands. 



Haemoglobin decomposes hydrogen peroxide, and 

 sets oxygen free. 



In contact with alkalies and acids, oxyhaemoglobin 

 is resolved into protein compounds, small quantises of 

 fatty acids, and a coloring-matter, hcematin, which, 

 when dried, has a grayish-brown color, and contains 9 

 per cent, of iron. Its composition can perhaps be ex- 

 pressed by the formula, C 34 H 34 FeN 4 5 . Haemoglobin 

 containing no oxygen gives another very unstable 

 coloring matter, haemochromogene, which takes up 

 oxygen with great avidity, and is converted into 



