ADDITIONS AND NOTES TO VOL. I. 489 



gests itself, whether a special pigment' (whose product of meta- 

 morphosis might be the well-known heematin, see p. 299) is here 

 merely added to the true crystalline substance, and either crystal- 

 lises with this substance as an isomorphous body, or only colours 

 it in the same manner as uric-acid crystals are commonly coloured 

 by the colouring matter of the urine, or whether we are here con- 

 sidering only a single ferruginous, crystallisable substance, of 

 which hsematin constitutes one of the separated products. I have 

 not yet been able decisively to determine this question, but 

 several facts seem to me to afford the greater amount of proba- 

 bility to the latter of these views. 



Products of its metamorphosis. These substances have not yet 

 been analysed with any satisfactory amount of exactness ; we will 

 therefore simply observe, that this protein-substance, precisely in 

 the same manner as albumen, after being treated with acetic acid 

 and alkaline salts, yields a substance which is altogether analogous 

 with Panum's acid albumen. The aqueous solution of this sub- 

 stance does not exhibit the slightest turbidity on boiling, but 

 when a larger or smaller quantity of an alkaline salt is added to it, 

 a precipitate will be formed at a lower or higher temperature, pre- 

 cisely the same as in the case of acid albumen. An excess of salt 

 precipitates this substance, even at an ordinary temperature; 

 hence we may obtain it entirely free from acid, after repeated 

 solution in water and precipitation by salts. When the solution 

 containing an acid is neutralised by potash or ammonia, a con- 

 siderable deposite is formed, which dissolves in ammonia, but is 

 precipitated from it at a gentle heat. Nitric and sulphuric acids 

 throw down copious precipitates from the aqueous solution, 

 but hydrochloric acid does not produce such an effect. Ferro- 

 cyanide of potassium occasions a considerable deposite without any 

 special addition of acid. Sulphate of magnesia, alurn, sulphate of 

 copper, chloride of iron, protochloride of tin, and neutral acetate 

 of lead do not produce any precipitates even by boiling, but 

 precipitates are thrown down by basic acetate of lead, nitrate 

 of silver, bichloride of mercury, and nitrate of protoxide of 

 mercury. 



I am still engaged in the analyses of this substance, as well as 

 in the investigation of other products of decomposition of the 

 crystalline substance. 



Preparation. The crystals of the blood, which may certainly 

 have been seen by many earlier investigators, but which were first 



