656 PHYSIOLOGICAL CHEMISTRY. 



the addition of water, which reduces the osmotic pressure of the 

 plasma, and consequently causes the salts of the corpuscles to attract 

 an excess of water, whereby the corpuscle is ruptured and its con- 

 stituents go into solution. In order to avoid this action on the blood- 

 cells and a similar action on the tissue cells, it is customary in sur- 

 gical procedures, and especially in intravenous injections, to use a 

 solution of equal osmotic pressure with the blood. Such a solution 

 is the "normal salt solution" made up usually of 0.9 per cent, sodium 

 chloride in distilled water, which is the simplest solution that has 

 been found to have no very deleterious effect. 



Blood-pigments. The haemoglobins or blood-pigments are the 

 chief constituents of red blood-corpuscles ; they contain from 0.4 to 

 0.6 per cent, of iron, and show a slight difference in composition ; 

 when in powder form they all have a blood-red or brick-red color; 

 they all crystallize, but not with equal facility. Hemoglobin is the 

 substance which carries oxygen to the various tissues, as described in 

 the previous chapter. It belongs to the class of conjugated proteins. 



Experiment 75. Pour some freshly drawn venous blood into four volumes of 

 a saturated solution of sodium sulphate contained in a vessel which stands in 

 ice ; mix and set aside for several hours ; no coagulation occurs and the cor- 

 puscles settle to the bottom of the vessel. Pour off the supernatant liquid, 

 collect the sediment on a filter, and wash it first with cold solution of sodium 

 sulphate and then with water. 



Prepare haemoglobin from these corpuscles as follows : agitate the collected 

 mass violently with small quantities of ether until the corpuscles are nearly 

 dissolved ; allow the liquid to settle, filter, render the filtrate slightly acid with 

 acetic acid, and add alcohol as long as the precipitate first formed continues to 

 dissolve ; cool the red solution to C. (32 F.) for several hours, when crystals 

 of haemoglobin will form ; collect these on a filter and wash with an ice-cold 

 mixture of alcohol and water. 



Hcemoglobin, also called reduced hcemoglobin, occurs only in small 

 quantity in arterial blood, in larger quantity in venous blood, and is 

 almost the only coloring-matter in the blood after asphyxiation. A 

 solution of hemoglobin has a most remarkable attraction for oxygen, 

 with which it enters into a molecular combination, forming oxyhazmo- 

 globin. The power of hemoglobin to take up oxygen depends on 

 the iron it contains. The solution of oxy hemoglobin will give up 

 oxygen to reducing agents or when subjected to a sufficiently low 

 oxygen pressure. It is due to this property of the oxyhernoglobin 

 that arterial blood gives up oxygen to the tissue. 



