6 A MANUAL OF VETERINARY PHYSIOLOGY 



mately either by the method of Gowers or Malassez. The 

 principle on which these methods are based is the same — a known 

 quantity of blood is diluted with a known bulk of artificial serum 

 and thoroughly mixed ; of this a small drop is placed in a counting- 

 chamber of known capacity, which is ruled into squares, and 

 examined under the microscope. The blood-cells occupying the 

 squares are counted, as may readily be done, and the mean of 

 them taken. In the horse the mean number of red blood- 

 corpuscles per cubic millimetre is 7,212,500, and in the ox 

 5,073,000. Taking the amount of blood in the horse as 29 litres 

 (50 pints, or 66 pounds), this gives 204,113,750,000,000 as the 

 approximate number of red cells in the body (Ellenberger).* It 

 is evident that a loss of water from the blood means a larger 

 relative proportion of red cells present, while an excess of water, 

 by diluting the blood, would show a loss of red cells ; thus the 

 number of the red cells is increased by sweating, by the excretion 

 of water from the bowels and kidneys, and by starvation, while 

 it is diminished by pregnancy and copious draughts of water. 

 But apart from these conditions, it is undoubted that an actual 

 increase or decrease in the number of red cells may occur, this 

 numerical variation being especially marked in some diseases. 

 The shape of the red cell is affected by the amount of fluid in the 

 plasma ; if the latter be artificially concentrated, water diffuses 

 from the corpuscle to the plasma, and in consequence it shrinks 

 and becomes wrinkled (Plate I.). If the plasma be diluted, the 

 red cells swell. A 0-9 per cent, solution of sodium chloride 

 causes the corpuscles neither to shrink nor swell ; this strength is 

 known as ' physiological salt solution,' and may be employed for 

 the purpose of transfusion. 



Each red cell offers a certain absorbing surface for oxygen, 

 which, if calculated on the total number of corpuscles, is some- 

 thing enormous, being equal for the horse to a square having a 

 side of 164 metres (180 yards). The opacity of blood is due to 

 the red cells reflecting light as the result of their peculiar shape ; 

 if the cells be destroyed, the blood becomes transparent or, as 

 it is termed, ' laky,' of which more will presently be said. 



The greater part of the red cell consists, as already stated, of 

 haemoglobin, a substance possessing a remarkable affinity for 

 oxygen ; this it obtains at the lungs, and leaves behind in the 

 tissues. The haemoglobin of the red cells, therefore, exists in 

 two states, one in which it is charged with oxygen called ' oxy- 

 hemoglobin,' and the other in which it has lost its oxygen and 

 is known as ' reduced haemoglobin.' The process of oxidation in 

 the lungs and reduction in the tissues is constantly occurring at 

 every cycle of the circulation, with the ultimate result that the 



* ' Physiologie der Haussaugethiere.' 



