CRYSTALLIZED OXYH^MOGLOBIN. 119 



the same with pure blood, and spread the products on a 

 piece of porcelain. Notice that the pure blood gives a 

 brown color, with a shade of green. The carbon monoxid 

 blood has a bright-red color on porcelain. This is a useful 

 test in cases of suspected poisoning by carbon monoxid. 



256. Prepare crystals of oxyhsemoglobin by placing on a 

 microscope-slide a drop of blood (one which crystallizes easily, 

 like that of a dog, rat, or guinea-pig) and cover it with a drop of 

 Canada balsam. Cover the whole with a cover-glass and examine 

 it under the microscope. The crystals will form in a few minutes. 

 They can also be made by mixing the drop of blood with a 

 small drop of water on the slide and allowing it to evaporate 

 until a dry ring has formed around it. Place a cover-glass over it 

 and it will crystallize. It is well to examine several different 

 species of blood if they can be obtained, such as guinea-pig, which 

 gives crystals in the form of tetrahedra (four-sided) ; mouse, giv- 

 ing six-sided plates; cat or dog, giving four-sided needles. 



257. A large quantity of crystallized oxyhsemoglobin can 

 be prepared by the following method: Make a solution of salt 

 containing 1 volume of saturated salt solution to 9 volumes of 

 water. Add 10 volumes of this to 1 of defibrinated blood, and 

 let it stand a day or two in shallow, flat-bottomed vessels until 

 the corpuscles have settled. Pour off the clear liquid, rinse the 

 corpuscles into a separatory funnel with the aid of as small a 

 quantity of water as possible, and add about as much ether. 

 Shake, but not too violently, separate the solution of oxyhsemo- 

 globin from the ether, and filter the former. Cool it to and 

 mix it with one-fourth its volume of alcohol which has been 

 also cooled to 0. Let the mixture stand at a temperature of 

 2 to 10 for several days, until the oxyhsemoglobin has 

 crystallized. This occurs with the blood of dogs and rats almost 

 immediately, but that of the ox crystallizes with much more diffi- 

 culty. After crystallization filter off the crystals in the cold, and 

 dry by pressing between filter-paper. The crystals may be purified 

 by dissolving in a small amount of water, cooling and precipitating 

 in the same manner, repeating several times. The crystals can be 

 preserved for a standard in the determination of the quantity of 

 oxyhsemoglobin in blood. 



