310 THE BLOOD. [CHAP. XXVTI. 



bulk, it will be found to deposit hsematine as a dark or black 

 powder. 



This haematine is insoluble in water, alcohol, or ether, unless 

 mixed with some alkali, which renders it readily soluble : when 

 burned it yields a considerable quantity of iron. 



Mulder's ultimate analysis gives the following as its compo- 

 sition : 



Carbon . . . . 65*84 



Hydrogen . . . . 5 '37 



Nitrogen .... 10*40 



Oxygen .... 11-75 



Iron ..... 6-65 



Much difference of opinion exists among chemists, as to the 

 state in which iron exists in the blood. We have already referred 

 to the opinion of Liebig, who affirms that, in venous blood, it is in 

 the state of protoxide, while, in arterial blood, it is in that of 

 peroxide; that the change of colour, from the dark red of the 

 former, to ,the bright scarlet of the latter, is due to the conversion 

 of the protoxide of iron into peroxide by the absorption of fresh 

 oxygen at the lungs. Mulder supposes that it exists in the 

 metallic state as a simple ingredient, as essential to the colour as 

 its oxygen, its hydrogen, its carbon, or its nitrogen. Scherer's 

 experience however, would go to show that iron is not essential to 

 the colour of the blood. He treated the red particles with sul- 

 phuric acid, so as to remove their iron, and found that their 

 colour still remained. Hence he infers that iron is not essential 

 to the colour. 



The value of the administration of iron in the treatment of cases 

 of anaemia after loss of blood, is well known and highly appreciated 

 by practitioners ; it remains to be determined in what way it con- 

 tributes so powerfully, as it unquestionably does, to the restoration 

 of the blood to its normal state. The fact that it does exercise a 

 powerful influence evidently indicates its importance as an ingre- 

 dient in the hsematine. And it may be remarked that iron, even 

 if not essential to its colour, may, nevertheless, be an essential 

 ingredient of a normal haematine. 



Difference of Arterial and Venous Blood. The prominent differ- 

 ence between blood drawn from the arteries and that from the 

 veins, is to be found in the bright scarlet colour of the former, and 

 the dark red, almost black, of the latter. To which may be added 

 some difference of temperature, that of arterial being one or two 

 degrees higher than venous ; perhaps also some difference as to 



