112 THE BLOOD. 



pig, and rat, but with more difficulty from human blood or 

 ox-blood. The color of the crystals is a bright red, and 

 their solution is a much brighter red than that of haemo- 

 globin, which, when pure, approaches a black. 



Oxyhaemoglobin is formed by the union of a molecule 

 of oxygen with one of hemoglobin, and it can without 

 difficulty be changed back into haemoglobin. The molecule 

 of oxygen is in this compound very loosely united. Oxy- 

 haemoglobin may be also considered as composed of an iron 

 compound, haematin, with an albuminous substance. It is 

 decomposed into these two substances when its solution is 

 heated, this change being hastened by acids or alkalies. 

 When heated with glacial acetic acid and a little sodium 

 chlorid it is decomposed, the haematin uniting with the nas- 

 cent HC1 formed at the same time and giving haemin, the 

 microscopic crystals of which have a brown color and char- 

 acteristic form. This is one of the best proofs for the 

 presence of blood, although it does not distinguish between 

 the different kinds. No other known substance gives 

 crystals of this color and shape. 



The spectrum of oxyhaemoglobin consists of two dark 

 bands: a narrow one at the right of the D line in the 

 yellow and a broader and less distinct one in the green 

 at the left of the E line of the solar spectrum. They can 

 be made to vary in width as well as distinctness by mak- 

 ing the solution more or less dilute. They can be per- 

 ceived when it contains 1 gramme of oxyhaemoglobin in 

 10 liters of water; that is, 1 part in 10,000. If to this 

 solution is added a few drops of ammonium sulphid, which 

 has a reducing action, the oxygen is removed and in a few 

 minutes the one broad band of haemoglobin is seen in that 

 part of the spectrum between the two oxyhsemoglobin 



