Colouring Pttnciple of the Blood. 315 



Greyish-brown flocculi were thus separated; and a muddy 

 colourless fluid remained, in which phosphoric acid and corro- 

 sive sublimate demonstrated the presence of serum. The pre- 

 cipitate, when collected on a filter and well washed, and half 

 dried, recovers its red colour, particularly when viewed by 

 transmitted light. When entirely dry it appears black, but when 

 a thin slice is held between the eye and the light, the colour is 

 garnet red. In this state it is hard, not easily broken, and has 

 a shining fracture. It consists of the colouring particles in a 

 state of perfect purity, but modified by heat. 



In this state, the colouring matter of the blood is insoluble in 

 hot or cold water, or in ether, and yields only a little fatty matter 

 to alcohol. Sulphuric, hydrochloric and phosphatic acids dissolve 

 a part, and form brownish-red solutions ; nitric acid also dissolves 

 a part, but the solution is muddy, and the residue is likewise al- 

 tered in colour ; phosphoric acid has no effect any more than on 

 the colouring matter in its ordinary impure unmodified condi- 

 tion ; acetic, citric, oxalic, and tartaric acids dissolve a little 

 with the aid of heat. The alkalis, with the aid of gentle heat, 

 dissolve it rapidly and completely, and form deep blood-red solu- 

 tions, which yield greyish brown flocculi when neutralized ; the 

 carbonated alkalies have little effect. 



The colouring particles, when not modified by the foregoing 

 process, but simply separated from the serum as much as possi- 

 ble by Berzelius^s method, are variously acted on by the gases. 

 Agitation in air makes them scarlet-red ; and this change is pro- 

 duced even after arterial blood has become dark by standing in 

 repose, nay, even also after it has begun to decay. In hydro- 

 gen, carbonic acid, nitrogen, nitrous oxide, olefiant, or sulphu- 

 retted hydrogen gas, the colour, on the contrary, becomes dark- 

 er, if it is changed at all. A stream of nitric oxide transmitted 

 through a diluted solution in water, makes it brown, and subse- 

 quently causes gelatinization. Sulphuretted hydrogen, in the 

 same way, makes it olive-green ; sulphurous acid, brown ; and 

 chlorine first makes it brown, then dirty green, next grey, and 

 lastly white ; and a flocculent colourless precipitate falls down, 

 leaving a colourless fluid. 



2. These observations conclude the iSrst part of the inquiry. 

 The next part relates to the presence of iron in the colouring 



