ELEMENTARY CHEMICAL PHYSIOLOGY 243 



ties believe that the haemoglobin is merely contained in a colloidal 

 state in a protein envelope. 



Chemically they contain about 60 per cent, of water and nearly 

 33 per cent, of haemoglobin, and varying amounts of lecithin, 

 cholesterol, nucleo-protein and salts. 



Haemoglobin. This is a compound protein containing 04 per 

 cent, of iron. When decomposed by acids or alkalis it splits up 

 into a protein of the nature of a histone (see p. 198) called globin 

 and into a pigment called heematin, which contains all the iron. 

 A pure solution of haemoglobin can be obtained by centrifugalising 

 blood, 1 removing the serum with a pipette, shaking up the cor- 

 puscles with a 0-85 per cent, sodium chloride solution 2 (which is 

 nearly isotomc for the blood of the ox, horse, or man), and again 

 centrifugalising. 



By this means the corpuscles are thoroughly washed free of 

 serum, etc. They are then collected and treated with two or three 

 times their bulk of distilled water, in this the haemoglobin dissolves, 

 a deep red solution resulting. The corpuscles have become * ' laked. ' ' 



EXPERIMENT VIII. Heat carefully some haemoglobin solution. 

 It decomposes at about 60 C., and the protein coagulates on further 

 heating. Also test the solution for protein ; it gives several of the 

 ordinary protein reactions, but in each case a splitting into protein 

 and haematin simultaneously ensues. 



Besides being dissolved out by distilled water the haemoglobin 

 may be set free from the red corpuscles by (i) warming to 50 C. ; 

 (ii) the addition of a little ether, or of dilute ammonia solution ; 

 (iii) the addition of bile, saponin, or the serum of another species 

 of animal. 



That haemoglobin contains iron can be shown by the following 

 experiment : 



EXPERIMENT IX. Dissolve some dried blood by heating with 

 strong nitric acid. Evaporate nearly to dry ness in a dish. Dis- 

 solve in water and add potassium sulphocyanide solution. A blood - 

 red colour indicates the presence of iron. 



Crystals of haemoglobin. These are most easily obtained from such 

 animals as the rat or guinea-pig ; with more difficulty from man 

 and most other mammals. 



EXPERIMENT X. Mix a drop of rat's blood with a drop of water 

 upon a slide. After several minutes examine under the microscope 

 for haemoglobin crystals. 



Haemoglobin, as we have seen, is a compound protein consisting 

 of two parts, the iron containing portion " hcematin " and the pro- 

 tein portion " globin." Haematin has the formula C 33 H 33 N40 5 Fe. 

 It itself does not crystallise, but a compound of haematin with 



1 Horses' blood should be used for this purpose as the corpuscles sink more 

 quickly than do the corpuscles of any other blood. 



2 A salt solution of this strength has the same osmotic pressure as the 

 contents of the red blood corpuscle, and consequently no swelling or crenation 

 of the corpuscle is produced. 



