102 
A TREATISE ON ELEPHANTS. 
carbonate and phosphate of sodium. Calcium, potassium and 
magnesium also occur in small amounts. 
White cells are of different varieties. Their most important 
function is the removal of useless and effete tissues, dead micro- 
organisms, etc. They may be looked upon as the scavengers of the 
body. 
Red cells are circular biconcave discs devoid of a nucleus as a 
rule. Their colour is due to an iron-containing substance called 
haemoglobin. Haemoglobin possesses the property of taking up 
oxygen from the air and of giving it up to the tissues ; it thus acts 
as the middleman between the air and the tissues. In certain 
diseases the number of red cells or the amount of haemoglobin in 
the red cells is reduced, and the animal is said to be anaemic. 
Lymph. — Lymph is the fluid which acts the pairt of middleman 
between the blood and the tissues. All the tissue spaces are filled 
by it, and every little cell is bathed by it. The tissue spaces open 
into lymph vessels through which the lymph flows to the lymph 
glands and thence back to the blood. In composition, lymph 
resembles somewhat the blood plasma, but it contains only a few 
white cells which are small in size and are known as lymph cells. 
Lymph is a straw-coloured fluid, but in the lymphatic vessel 
coming from the digestive canal after a meal it has a milky appearance, 
due to the presence of fats in a very fine state of division which have 
been absorbed from the intestine. 
Lymph is derived partly from the blood and partly from the 
tissues. 
Circulatio7i. — The means by which the blood and lymph are 
distributed to the tissues consists of a central force pump,, the heart, 
and a series of tubes, the arteries, which lead to all parts of the 
body and terminate in innumerable fine tubules, called capillaries, in 
the substance of the tissues. From these capillaries a certain 
proportion of the blood constituents escape into the spaces between 
the cells as lymph. This lymph is carried away in a series of 
lymph vessels passing through the various tissues and organs to the 
lymph glands, and from there back to the heart by w^ay of the veins. 
During its passage through the tissues the lymph is deprived of 
much of its nutrient material, receiving in return the waste products 
of tissue metabolism. The remainder of the blood, which has not 
passed out of the capillaries as lymph, has thus been deprived of 
some of its nutrient material ; this is made up for by a part of the 
blood being sent through the walls of the stomach and intestine 
where nutrient material from the food is taken up by the blood 
returning to the heart. In addition to this nutrient material the 
blood returning to the heart contains waste products, the result of 
