864 PHYSIOLOGY 



The stroma protein forms only about 4 per cent, of the total solids of 

 the corpuscle. It is insoluble in dilute acids, but easily soluble in dilute 

 alkalies. On gastric digestion the greater part dissolves, leaving a residue 

 which is rich in phosphorus, and has been called nuclein. Stroma protein is 

 therefore spoken of as a nucleo-protein. Wooldridge, who devised the 

 method given above for the preparation of pure stromata, regarded the 

 protein as a compound of protein and lecithin. The substance certainly 

 contains a large quantity of lecithin, the greater part of which is present in 

 the precipitate obtained on gastric digestion. According to Wright the 

 nuclein residue yields purine bases on hydrolysis, and is therefore rightly 

 classed with the other nucleins from tissue cells and contained in nuclei. 



From the laked solution of corpuscles, oxyhaemoglobin can be ob.tained in a crystalline 

 form with varying readiness according to the animal from which the blood is derived. 

 Thus in the case of the rat, the guinea-pig, the dog, and the horse it is sufficient merely 

 to cool the laked blood, preferably in a freezing mixture to about 10 C. in order to 

 obtain a large crop of haemoglobin crystals. Crystallisation is facilitated by the addi- 

 tion of 25 per cent, of absolute alcohol to the mixture, though the use of alcohol certainly 

 tends to interfere with the subsequent purification and solubility of the haemoglobin. 

 Oxyhsemoglobin can be re'crystallised by dissolving it in weak alkali at 35 C., cooling 

 the solution to C., and then adding cold alcohol to 25 per cent, and allowing the 

 mixture to stand for some days at a temperature of 5 to 10 C. In the case of 

 those bloods which yield oxyhaemoglobin crystals with greater difficulty, it is better to 

 add to the laked blood an equal volume of a saturated solution of ammonium sulphate. 

 The precipitate of globulins is filtered off and the filtrate allowed to stand in a cool 

 place. Crystals of haemoglobin then come down in quantity. 



PROPERTIES OF HAEMOGLOBIN 



The crystals thus obtained are as a rule microscopic in size. Most 

 animals yield an oxyhaemoglobin which crystallises in rhombic prisms or 



needles belonging to the rhombic system. 

 In the guinea-pig the crystals are tetrahe- 

 dral in form, while the oxyhaemoglobin of 

 the squirrel crystallises normally in the 

 form of six-sided plates. On recrystaUi- 

 sation however, a squirrel's haemoglobin 

 can be obtained as a mixture of rhombic 

 prisms with rhombic tetrahedra. The 

 water of crystallisation of oxyhaemoglobin 

 Fia. 371. Crystals of oxyhaemoglobin. var i es i n different animals between 3 and 

 1. From rat.^2. From guinea-pig. 9 per cent> The so l u biHty of the crystals 



differs according to the animal from which 



they have been derived, and is in direct proportion to the difficulty with 

 which the crystals are obtained. They are more soluble in highly diluted 

 solutions of ammonia and the caustic alkalies and their carbonates than in 

 water. A solution of haemoglobin will not diffuse through parchment paper ; 

 the elementary analysis of oxyhaemoglobin crystals gives somewhat varying 



