During the war, the “Red Ball Blood Test” was used as a quick test on the battle lines. If a soldier claimed to be sick, they pierced his finger with a needle for a drop of blood. If a “red ball” appeared, the soldier would be handed his rifle and sent off to battle.

If the blood layer on the finger looked watery and not bright red, the solder was deemed ill, and would usually not be sent off to fight.

This test could quickly determine an individual’s overall health.

MORE ABOUT BLOOD AND ITS COMPONENTS

Blood is the fluid that circulates through the heart, arteries, capillaries, and veins. It is the chief means of transport within the body. It transports oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. It transports nutrients and metabolites to the tissues and removes waste products to the kidneys and other organs of excretion.

Blood has an essential role in the maintenance of fluid balance.

The total blood volume for an average adult is about 5 litres, approximately 8{0ad5881c2192913025db5bf2180b2e0b17ede26560c7c351a451156c0b06bc98} of the total body weight.

Blood varies in colour from an oxygenated bright red in the arteries to a duller red in the veins.

The blood can be divided into two main components: the liquid portion (plasma) and the formed elements (blood cells). Plasma accounts for about 55{0ad5881c2192913025db5bf2180b2e0b17ede26560c7c351a451156c0b06bc98} of the total blood volume. It consists of about 92{0ad5881c2192913025db5bf2180b2e0b17ede26560c7c351a451156c0b06bc98} water, 7{0ad5881c2192913025db5bf2180b2e0b17ede26560c7c351a451156c0b06bc98} proteins and less than 1{0ad5881c2192913025db5bf2180b2e0b17ede26560c7c351a451156c0b06bc98} inorganic salts, organic substances other than proteins, dissolved gasses, hormones, antibodies and enzymes. The formed elements (blood cells) of the blood comprise the other 45{0ad5881c2192913025db5bf2180b2e0b17ede26560c7c351a451156c0b06bc98} of the total blood volume. These formed elements are produced in the bone marrow and include erythrocytes (red blood cells), leukocytes (white blood cells) and thrombocytes (platelets).

The normal pH of the blood is maintained at about 7.35.

The blood is a very sophisticated colloidal system that is absolutely essential for life. It performs many important functions, including:

Blood supplies oxygen to the body cells.
It delivers nutrients such as glucose, amino acids and fatty acids to the body cells.
It removes waste such as carbon dioxide, urea and lactic acid from the tissues.
It is involved with immunity in that it circulates leukocytes and antibodies.
It plays a central role in repair through the process of coagulation.
Circulating blood is important in several messaging systems in the body (e.g. hormones, chemical messengers such as leukotrienes).
It helps to maintain the normal, narrow pH range of 7.35 to 7.45.
Blood and its distribution within the body help to regulate the core body temperature.
Blood plays a role in hydraulic functions in the body.