472 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



CHROMOPROTEINS. 



The only well-defined member of this group of conjugated proteins 

 is haemoglobin, which is composed of the coloured substance haematin 

 or haemochromogen (p. 482) and the protein globin. The substance 

 haemocyanin, which is found in the blood of molluscs and Crustacea, 

 has been regarded as a similar conjugated protein, but more recent 

 work does not confirm the older idea. Haemocyanin contains copper 

 in the place of iron in the coloured moiety of its molecule. 



Haemoglobin. 



Haemoglobin is present in the blood of all vertebrate animals and 

 of some invertebrates. It is found either in solution in the liquid or 

 more usually is contained in the red blood corpuscles, from which it can 

 easily be separated. It is present in muscular and nervous tissue 

 and under pathological conditions appears in the urine and faeces. 



The haematin portion of haemoglobin seems to be the same in all 

 animals, but the protein portion may be different. 



The haemoglobin in the red blood corpuscles of the higher animals 

 has been chiefly investigated. The red blood corpuscles can be 

 separated from blood which has been prevented from clotting, e.g. 

 by oxalates, or from defibrinated blood by centrifugalisation. Most 

 of the properties and reactions of haemoglobin can be easily studied 

 directly with blood or defibrinated blood so that its isolation is not 

 essential. 



BLOOD. 



(1) Reaction. 



Blood is alkaline in reaction to litmus and methyl orange ; it is acid 

 to phenol phthalein. The alkalinity is due chiefly to disodium phos- 

 phate and corresponds to -4 per cent, or -I N sodium hydroxide. 



The alkalinity to litmus is easily seen by placing a drop of blood 

 upon a piece of neutral glazed litmus paper and in 10-30 seconds 

 washing off the blood with distilled water ; a blue mark remains. 



(2) Specific Gravity. 



The specific gravity of human blood is usually from 1054-1060, but 

 values of 1040 and 1065 have been observed. The specific gravity 

 of defibrinated blood usually varies from 1050-1055. 



Determination. 



The specific gravity can be determined by weighing against an 

 equal volume of water. 



