192 THE BLOOD. 



crystals ma}' be diluted by the addition of an equal volume of 

 a mixture consisting of one part of ninety per cent, alcohol and 

 four parts of distilled water. The whole must be filtered 

 through calico, and the soft haemoglobin freed from the greater 

 part of the adhering water and spirit by being placed on a 

 porous brick and exposed to a current of cold air. Whichever 

 method of separating the crystals is used, they must be purified 

 by recrystallization. 



The best method of obtaining haemoglobin crystals in small 

 quantities, for microscopical purposes, is one founded on the 

 same principles. A teaspoonful of defibrinated blood is treated 

 with a sufficient quantity of water to render it transparent. 

 A quarter of its bulk of alcohol having been added to it, the 

 mixture is introduced into a platinum capsule, and plunged in 

 a mixture of pounded ice and salt. A relatively abundant 

 crop of crystals is obtained. The mere freezing and thawing 

 the blood, as directed in 11, will also give satisfactory re- 

 sults. Another method consists in passing the vapor of chloro- 

 form through the blood, which has alwa} r s the effect of render- 

 ing it laky, and in some animals determines crystallization. 



17. Chemical Properties of Haemoglobin. Solubility. 

 The solubility of haemoglobin in water differs according to 

 the species of animal from which it is derived. Thus the color- 

 ing matter of the dog and cat are very soluble at 40 C.; 

 sparingly soluble in ice-cold water. That of the guineapig 

 dissolves with relative difficulty at all temperatures, and crys- 

 tallizes more readily than that of any of the common domestic 

 animals. All kinds of haemoglobin are more soluble in warm 

 water than in cold. Diffusibility. Haemoglobin, although 

 crystallizable, is indiffusible. This can be easily shown by 

 placing a solution of blood or haemoglobin in a diffusion-cell, 

 the septum of which is of good parchment paper. 1 If an animal 

 membrane is substituted, a certain amount of coloring matter 

 passes from the solution into the water. The fact of the 

 diffusibility of haemoglobin perhaps stands in relation with 

 the enormous weight of its molecule. Coagulability. Aque- 

 ous solutions of haemoglobin coagulate when heated, just in 

 the same way as albumin, and at about the same temperature 

 (64 C.). When this occurs, the haemoglobin splits into an 

 albuminous compound and an insoluble coloring matter. Pre- 

 cipitation by Alcohol. Small quantities of alcohol may be 

 added to solutions of blood or haemoglobin without producing 

 any appreciable change. In continuing the addition a precipi- 

 tate is formed, which at first is redissolved on shaking, after- 

 wards becomes permanent. Relation to Oxygen. In a solution 



1 For method of preparing and testing a diffusion-cell, see Chapter 

 on Chemical Methods. 



