Blood has been known to be essential for life since the earliest times.  It was considered to be the essence of life, and was also thought to determine our character and emotions.  Anger was said to make our blood "boil" and fear caused "curdling" of the blood. 

The Catholic Church in 1492 attempted to restore to life the dying Pope Innocent VIII by having him drink the blood of three youths whom Church authorities had slaughtered like sacrificial cows for this purpose.  Obviously the treatment was a failure and the Pope died shortly afterwards.

Similar to these practices of the Catholic Church, was the case of the Countess Elizabeth Bathory, the Blood Countess of Castle Csejthe, in Hungary.  She believed blood was capable of restoring and beautifying skin and she had her servants kill and drain blood from female virgins to provide her with a daily bath in blood.  For ten years the countess indulged herself until 1610, when the King ordered an investigation into her affairs prompted by the scarcity of virgins in the area.  Along with the skeletons, the soldiers found the body of a young female freshly killed and drained of blood. In punishment the "Blood Countess", was walled up in her bedchamber where she died four years later.  We have no record as to the effectiveness of her beauty treatments.

The end of such horrific practices was heralded by the revolution in knowledge about the physiology of blood that occurred in the seventeenth century due primarily to the efforts and observations of the Englishmen William Harvey, a court physician to James the first and Charles the first.

A French physician performed the first blood transfusion on a human in June 1667, Jean - Baptiste Denys the blood for the transfusion was drained from a lamb and was injected into a 15-year-old boy who apparently suffered no ill effects. Although blood transfusions were developed in Western Europe, it was not first performed there. It is believed that the Incas regularly practiced blood transfusion centuries before the Europeans invaded their land.  Problems with incompatibility would have been minimal for the south American Indians are generally of blood group type O -Rhesus positive.

Blood is frequently mentioned in scripture:

Exd 12:13 And the Blood shall be to you for a token upon the houses where you are: and when I see the Blood I will pass over you and the plague shall not be upon you when I smite the land of Egypt.

Lev 17:11 For the life of the flesh is in the Blood: and I have given it to you to make an atonement for your souls,for it is the blood that makes an atonement for the soul.

Jhn 6:53 Then Jesus said unto them verily I say unto you except you eat the flesh of
The son of man and drink his Blood you have no life in you.

Jhn 6:54 Who so eateth my flesh and drinketh my Blood has eternal life and I will raise him up at the last day. 

Mat 27:4 I have sinned  in that I have betrayed the innocent Blood.

Mat 26:28 For this is my Blood of the new testament for the remission of sins.

Hbr 9:22 And almost all things are by the law purged with Blood and without shedding of blood there is no remission.

Hbr 9:14 How much more shall the Blood of Christ who through the eternal spirit without spot to God, purge your conscience from dead works to serve the living God?

Hbr 9:12 Neither by the Blood of goats and calves but by his own Blood He entered in once into the holy place having obtained eternal redemption.

Pe 1:19 But with the precious Blood of Christ is a lamb without blemish and without spot.

Rom 5:9 Much more than, being now justified by his Blood we shall be saved from wrath through him.

Eph 2:13 But now in Christ Jesus ye who was sometimes were far off are made nigh by the blood of Christ.

Col 1:14 In whom we have redemption through his Blood, even  the forgiveness of sins.

Blood is a type of connective tissue with cells suspended in plasma.  The functions of blood are grouped as transportation of gases, nutrients, electrolytes, water and vitamins, maintenance of homeostasis (constant internal environment), and finally protection against foreign substances such as microorganisms and toxins.  Blood Clotting also provides protection against blood loss after vascular injury.

The average human body contains 4 to 6L of blood and this forms approximately 8% of the body weight.  If a blood sample is taken, the cells can be separated from the plasma by spinning the whole blood in a centrifuge.  The cellular elements occupy about 45% of the volume of blood and settle to the bottom of the centrifuge tube, forming a dense red pellet. Above this cellular pellet is a pale yellow fluid called plasma. About 95% of the volume of the cellular elements consists of erythrocytes or red blood cells. The remaining five percent consists of white blood cells and the platelets. 

Plasma consists of about 91% water, 7% proteins and other solutes, which account for 2%.   The main plasma proteins are Albumins (58%), Globulins (38%) and Fibrinogen (4%).  

Albumin plays an important role in maintaining the osmotic concentration of blood.   Globulins are part of the immune system and fibrinogen is responsible for the formation of blood clots.  Other solutes in the plasma include ions,nutrients, waste products, gases and regulating substances.  The plasma volume remains relatively constant.  Water intake closely matches loss through the skin, digestive tract, lungs and kidneys.

After birth, the cellular elements are formed in the red bone marrow.  In young children nearly all marrow is red marrow, however in adults red marrow is confined to the skull ribs, sternum, vertebrae, pelvis, proximal femur and humerus. 

Of the cellular elements,the red blood cells are about seven hundred times more numerous than white cells and seventeen times more numerous than platelets. Males have about 5.2 million red blood cells per cubic mm of blood while females have about 4.5 million red blood cells per cubic mm of blood.  Each red blood cell has a diameter of 7.5 micrometers and is a bi concave disc (the edges are thicker than the center).  The biconcave shape increases the surface area, which makes the movement of gases in and out of the cell more rapid.  In addition the red blood cell can bend and fold around a thin center decreasing its size and enabling it to pass through small vessels. The main component of the cell is the protein hemoglobin, which occupies about one third of the total cell volume and accounts for the red color.  The primary function of hemoglobin is transport of oxygen.  98.5% of the oxygen transported in the blood is in combination with hemoglobin and approximately 1 - 5% is dissolved in plasma.  Each hemoglobin molecule consists of four protein chains, and four heme groups.  Each heme group contains one iron atom.  Fetal hemoglobin is replaced by adult hemoglobin near the time of birth.  Fetal hemoglobin is more efficient in binding oxygen than adult hemoglobin therefore facilitating oxygen supply during pregnancy.

Various poisons affect the hemoglobin molecules.  Carbon Monoxide binds to the iron of hemoglobin forming a stable compound called Carboxyhemoglobin.  As a result of this binding,hemoglobin cannot transport oxygen and death may occur.  Carbon Monoxide occurs in incomplete combustion of gasoline.  Cigarette smoke also produces carbon monoxide and the blood of smokers can contain 5 to 15 % carboxyhemoglobin. 

Under normal conditions about 2.5 million red blood cells are destroyed every second.   This however is only 0.00001% of the total 25 trillion red blood cells in the adult circulation.  This 2.5 million cells destroyed by an equal number of red blood cells every second.

Erythrocytes stay in the circulation for 120 days in males and 110 in females.  Red blood cells lack nuclei and therefore cannot produce new proteins, ageing and dying as a result. 

Regulation of production is by means of a hormone produce in the kidney eryrthropoietin.  

In contrast the red blood cells, the white cells are clear colored cells, have a
Nucleus and lack hemoglobin.  There are five types, neutrophils, lymphocytes, monocytes, eosinophils  and basophils  in order of decreasing frequency.   White cells protect in invading microorganisms and remove dead cells and debris from the cell. Normally a cubic mm of human blood has 5000 to 10 000 white cells.   The number increases temporally in infections. 

The third cellular element of blood is the platelets. These are fragments of cells 2 to 3 micrometers in diameter; they have no nuclei and are important in blood clotting.   There are usually 250 000 to 400 000 platelets per cubic mm of blood.

Individuals are divided into four major blood types depending on the polysaccharide antigen on their surface: A, B, AB and O.  In the US 45% are O, 41% A, 10% B and 4% AB.  People with blood group AB are called universal recipients and can receive blood of any type.  Type O individuals are called universal donors and they can donate blood to anyone without causing a transfusion reaction.

God has revealed himself in two books: The book of nature and the book of scripture.   The study of creation should lead the creature to the creator, and as Calvin stated "Man must put on spectacles if he is to read the book of nature correctly. Even the most basic physiological account of the blood, as given in the above short article, should lead the creature to the creator providing the creature has not thrown away his reading spectacles."