222 PHYSIOLOGICAL CHEMISTRY. 



the minimum molecular weight which may be calculated from 

 this analysis is : 



It is interesting to note that the molecular weights found 

 in this way are practically confirmed by the determinations 

 made on the combining power of hemoglobin for carbon mon- 

 oxide. Assuming that one molecule of carbon monoxide is 

 held by one molecule of hemoglobin, observations of the vol- 

 ume of the gas absorbed by a given weight of the blood pig- 

 ment lead to practically the same result as was obtained by 

 the iron method. 



Combinations of Hemoglobin. The great importance of 

 hemoglobin depends on its power of forming several more or 

 less stable combinations with certain gases. Of these combi- 

 nations that with oxygen is by far the most important; we 

 distinguish therefore between hemoglobin and oxyhemoglobin. 

 The common form of the substance is really the latter, al- 

 though it is usually referred to by the simple term hemo- 

 globin. The oxygen of oxyhemoglobin is very loosely held 

 and may be driven out from its union by the aid of a current 

 of other gases, or by the pump. The amount so held corre- 

 sponds to two atoms of oxygen for each molecule of hemo- 

 globin. This oxygen combining power in some way depends 

 on the presence of the iron of the hematin. 



Oxyhemoglobin. By various methods this substance may 

 be obtained in crystalline form, the crystals being often 2 mm. 

 or more in length. From blood of different animals different 

 crystalline forms have been observed. In all cases the crystals 

 are red and soluble in water; they are more easily soluble in 

 water containing a little sodium carbonate. They are insolu- 

 ble in ether, benzene and chloroform, and the water solubility 

 varies with the nature of the blood from which they were 

 made. That from the blood of man and the ox, for example, 

 being easily soluble, while the oxyhemoglobin from the blood 

 of the horse or dog is rather slowly soluble. Because of their 

 solubility it is very difficult to secure crystals from human 

 blood, but from dog's blood they may be made as follows : 



