THE BLOOD 



The Red Corpuscles constitute 33 per cent., or one- third of the 

 total blood. Viewed under the microscope, they are found to 

 be biconcave discs, circular in shape, and possessing no nucleus 

 (Plate I.) ; they are soft, flexible, elastic bodies, capable of having 

 their shape readily altered by pressure, which enables them to 

 pass along the finest capillaries. The colour of a single corpuscle 

 is yellow, but when heaped together they appear red, and thus 

 give the colour to the blood. ^ 



In all mammals, excepting the camel tribe, the red cells are 

 circular and biconcave ; in the Camelidae they are elliptical and 

 biconvex. In all vertebrates below mammals they are bi- 

 convex, oval, and nucleated (Plate I.). The corpuscles vary in 

 size in different animals, being smallest in the deer tribe and 

 largest in the elephant, 

 as may be seen in the 

 diagram (Fig. 1). When 

 a drop of blood is shed, 

 the red cells at first 

 move quite freely each 

 over the other. In a 

 short time they tend 

 apparently to become 

 sticky, and when this 

 state is reached they 

 have a tendency to lie 

 in long rows, with their 



flat surfaces in close contact, resembling the appearance of a 

 pile of pennies. This condition is not marked in horses' blood. 



A red blood-cell is composed of a spongy stroma, holding in its 

 meshes the red colouring matter. The stroma or framework of 

 the corpuscle consists of nucleo-albumin, lecithin, cholesterin, 

 and salts ; the red colouring matter, haemoglobin, forms no less 

 than 32 per cent, of the total solid matter of the fresh corpuscle. 



Great discussion has taken place as to whether the corpuscle is 

 a perforated mass of protoplasm containing no covering, or 

 whether it possesses a cell-wall, as its microscopical appearance 

 indicates. At present the general feeling is that there is no 

 cell-wall, but that there is a condensation of the cell-substance 

 at the periphery, while within the spongy substance of the 

 interior is lodged the haemoglobin, probably in an amorphous 

 condition, certainly not in a crystalline state, and perhaps not 

 in solution. It is further supposed that the large amount of 

 lecithin and cholesterin present in the stroma gives permeability 

 to the external layer of the cell. For example, water, alcohol, 

 ether, and a solution of urea can pass in, but not neutral salts. 



The number of corpuscles in the blood is determined approxi- 



Fig. 1. — Diagram showing Relative Size 

 of Red Corpuscles of Various Animals 

 (Stewart). 



