THE RED BLOOD-CORPUSCLES 927 



From such laked blood we may prepare either haemoglobin or 

 stroma. 



PREPARATION AND PROPERTIES OF THE STROMA. In order 

 to separate the stroma from the haemoglobin, blood which has been 

 defibrinated or prevented from clotting by the addition of a little 

 sodium oxalate is centrifuged until all the formed elements form 

 a solid cake at the bottom of the tube. The tube is then filled up 

 with normal saline fluid and again centrifuged, and this process 

 repeated twice in order to wash away adherent plasma or serum. 

 After the final washing two volumes of distilled water saturated with 

 ether are added to one volume of caked corpuscles. The corpuscles 

 swell up and their haemoglobin passes into solution into the surround- 

 ing fluid. The blood is laked. The fluid is once more centrifuged in 

 order to throw down white blood- corpuscles. A 1 per cent, solution 

 of acid sodium sulphate is now added drop by drop until the solution 

 acquires the opaque appearance presented by ordinary blood. The 

 action of this salt, as of dilute acids, is to precipitate the swollen-up 

 stromata, which reacquire the power of reflecting light from their 

 surfaces and restore the opacity to the blood. On centrifuging, the 

 stromata are thrown down, and can be collected and washed with 

 distilled water several times on the centrifuge. The stroma protein 

 only forms 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. 



PREPARATION AND PROPERTIES OF OXYH^MOGLOBIN. 

 From the laked solution of corpuscles oxyhaemoglobin can be 

 obtained 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 sufiicient 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 addition 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. Oxy- 

 haemoglobin can be recrystallised by dissolving it in weak alkali at 



