MILK, BLOOD AND URINE 221 



blood plasma which holds the erythrocytes in suspension is 

 made more dilute by the addition of water, an osmotic pressure 

 is produced within the erythrocytes due to the rapid inward 

 diffusion into the corpuscle of water from the plasma. This 

 pressure may become strong enough to rupture the cell wall of 

 the corpuscle, when the colored haemoglobin is discharged into 

 the plasma, leaving the corpuscles colorless. This general 

 action is termed Immolysis or taking, and may be produced also 

 by certain substances, e.g. ether, chloroform, bile, the toxins 

 of snake venom and of certain bacteria, and products produced 

 in the body by immunization. The osmotic pressure of blood 

 plasma is approximately equivalent to a 0.9 per cent solution 

 of sodium chloride and in such a solution no haemolysis takes 

 place. A salt solution of this strength is known as a physio- 

 logical salt solution or normal saline solution. 



The second special property of erythrocytes is that of agglu- 

 tination, or precipitation, when acted upon by certain substances. 

 The action is called hemagglutination. 



Hsemoglobin and Oxyhaemoglobin. — Haemoglobin, it will 

 be recalled, was mentioned, in the discussion of proteins, as 

 one of the conjugated proteins, consisting of a protein part (a 

 histon called glohin), together with an iron-containing colored 

 part known as hcemochromogen. The erythrocytes are oxygen 

 carriers, and it is this haemoglobin which is the essential con- 

 stituent of red blood corpuscles in the performance of this 

 function. Haemoglobin occurs in the venous blood, and when 

 it comes in contact with inhaled air in the lungs it absorbs 

 oxygen and is thereby converted into oxylicemo glohin in the 

 arterial blood. In the blood capillaries of the cellular tissue the 

 oxyhaemoglobin gives up its oxygen to the food nutrients, 

 which are thereby oxidized and energy liberated, the oxyhae- 

 moglobin in turn being reduced to haemoglobin. In this way 

 the haemoglobin, a constituent of red blood corpuscles, acts as 

 a carrier in conveying oxygen from the lungs to the muscle 

 cells. This action probably rests in the iron component of the 

 protein and is analogous to the bromine carrier property of 



