314 Engelhart on the 



% On the colouring principle of the Blood. 



In 1825, the medical faculty of Gottingen decided their 

 prize-question on the Nature of the Colouring Principle of the 

 Blood, in favour of the thesis of Dr Frederick Engelhart. His 

 experiments are very interesting, and estabhsh satisfactorily 

 some disputed points with regard to the composition of the blood; 

 but we cannot go altogether along with him in considering that 

 he has determined the colouring principle to consist of a com- 

 pound of iron. 



Two doctrines prevail at present among chemists and physi- 

 ologists as to the cause of the colour of the blood. The oldest 

 opinion is that it depends on iron ; and this opinion is believed to 

 derive support particularly from the late analytic inquiries of 

 Berzelius, who found a notable quantity of iron in the co- 

 louring particles, namely about 0.5 per cent. Others main- 

 tain the doctrine first proposed by Dr Wells, that the colour 

 is owing to a peculiar arrangement of the animal principles, in- 

 dependently of the presence of iron ; and their opinion receives 

 confirmation from the unsuccessful attempts of Vauquelin and 

 Brande to detect iron in the quantity in which it is represented 

 by Berzelius to exist. 



These contradictory statements and ideas being held in view, 

 Dr Engelhart proceeded to ascertain, in the first place, the cha- 

 racters of the pure colouring matter of the blood, and, secondly, 

 the relation which the three great principles of the blood bear to 

 one another, as to the quantity of iron they contain. 1. A preli- 

 minary object of investigation under the first head, was to separate 

 the colouring matter in a state of purity. This he succeeded 

 in doing by a new and very simple process ; but, although the 

 colouring particles certainly appear to be procured by his me- 

 thod in a state of perfect purity, it is equally certain that this 

 object is not gained without some change being wrought upon 

 their properties. He first separated them by the method of 

 Berzehus, in which state, however, they are still mixed with a 

 little serum. Having found that serum when much diluted is 

 not coagulated by heat, while, as Berzelius formerly showed, 

 the colouring particles are coagulated even in a very diluted so- 

 lution, he dissolved the impure particles in about fifty parts of 

 water, and then raised the temperature a little above 150° F. 



