190 THE BLOOD. 



undergoing chemical change, or in other words, any of the 

 methods by which the blood can be rendered transparent or 

 \aky, may be used for obtaining crystalline hemoglobin. Many 

 of these methods yield the product very readily, when the blood 

 is derived from one of those animals in which the coloring 

 matter is prone to crystallize. There are, however, only one 

 or two of them by which pure haemoglobin can be obtained in 

 considerable quantity. 



Thus by the method of freezing, large well-formed crystals 

 can be obtained from the blood of the guineapig or dog. In 

 like manner the blood of the same animals crystallizes readily 

 after it has been rendered laky by warming or by the trans- 

 mission of induction shocks. 



When it is intended to prepare considerable quantities in a 

 state of purity, it is best to emplo}- water as a solvent, and 

 then to determine crystallization in the liquid by the addition 

 of alcohol, in such proportions that the mixture is only just 

 capable of retaining the coloring matter in solution. To insure 

 success, it is to be borne in mind that the coloring matter 

 crystallizes as ox} r hoemoglobin (see 17), that crystallization is 

 much impeded by the presence of non-crystallizable organic 

 compounds, particularly albumin, and that haemoglobin is 

 prone to undergo change when exposed in solution to tempe- 

 ratures above that of freezing. To insure complete oxidation, 

 the blood must be freely exposed to air. To obviate the 

 interfering influence of albumin, the coloring matter must be 

 derived, not from the whole of the blood, but in as far as pos- 

 sible from the corpuscles alone. To obviate the risk of che- 

 mical change, i. e., of the splitting of the haemoglobin into 

 other products, the liquids must be subjected, as far as pos- 

 sible, during the whole operation to a low temperature. These 

 indications are fulfilled in the following process, devised by 

 Preyer, which gives good results, when the weather is cold 

 and when blood is used of which the coloring matter is com- 

 paratively insoluble in water at C., e. <?., that of the dog or 

 cat. The haemoglobin of the blood of the horse, on the other 

 hand, is very soluble at all temperatures. It cannot therefore 

 be prepared by Preyer's method. Blood to be employed is 

 allowed to flow from a vein or artery into a porcelain capsule. 

 It is then placed in a cool cellar to coagulate. On the follow- 

 ing day most of the serum is poured off, and the remainder 

 removed with the aid of a pipette. The clot is then cut into 

 small fragments and placed on a filter of fine calico, on which 

 it is washed repeatedly with ice-cold distilled water, until the 

 washings give scarcely any precipitate with a solution of cor- 

 rosive sublimate. [This indicates that the clot is tolerably 

 free from serum-albumin. The water must be ice-cold, because 

 at freezing temperature haemoglobin is sparingly soluble.] 



