CIRCULATION OF THE BLOOD. 61 
The liquor of the blood consists of water in which are dissolved a 
quantity of a substance called fibrine,! a good deal of albumen, to which 
all the tissue-forming elements of the food are reduced, a quantity of 
fatty matter, and other organic substances, with a quantity of mineral 
matter, principally salt. The fibrine is the substance which coagulates in 
the blood (it may be seen by beating fresh blood with a stick, to which it 
adheres in fine threads—hence its name); and it is this property that 
forms the beautiful provision for»the repair of injuries. Were it not for 
this power of coagulating, a great quantity of blood might be lost by the 
smallest cut or scratch. The purpose of the albumen, along with the fatty 
matter also in solution in the blood, is to be expended in keeping up the 
solid tissues of the body, by which it is being continually appropriated. 
The liquid in which the fibrine and albumen are dissolved has the power 
of absorbing gases, so that the ‘liquor of the blood, besides continually 
building up the tissues of the body, also conveys to them oxygen from 
the lungs, and carries back the carbonic acid which is set free in the 
tissues. But in this duty, the heaviest part of the work is performed by 
the properly solid part of the blood, the red corpuscles ; and these, again, 
besides this function, are principally concerned in the production and 
renewal of the muscular tissue. 
The apparatus by which the blood is conveyed to every part of the 
body, to perform the functions just described, consists of two systems of 
tubes to convey the blood, called blood-vessels, and the heart, which is in 
reality a force-pump of great power. The two sets of blood-vessels are the 
arterves, which carry the blood from the heart throughout the body, and 
the veins, which bring it back to the heart. There is, besides this, a 
second circulation. When the blood returns to the heart, it is unfit to be 
again sent out until it be purified by exposure to the air: this is accom- 
plished in the lungs, so that all the blood thus returned to the heart is 
immediately sent off to the lungs, from which it comes back to the heart ; 
and this is called the Pulmonary? or Lesser Circulation. There are thus 
two sets of arteries and two sets of veins, the vessels which carry the 
blood from the heart to the lungs, and vice versd, being called pulmonary 
arteries and veins respectively ; although it is to be remembered that the 
kind of blood contained in the arteries and.veins of the different sets is 
reversed, the pulmonary arteries containing true venous blood, and the 
pulmonary veins carrying back to the heart true arterial blood. 
The Heart is a strong muscular bag, situated in the left side’ of the 
chest. It contains four chambers or divisions, the two in the upper end 
called auricles * (d the right auricle, and & the left, fig. 54), and the two in 
1 From Latin fibra, a thread. 2 From Latin pulmones, the lungs, 
3 Latin auricula, diminutive of auris, the ear. ; 
