CHAMBERS'S INFORMATION FOR THE PEOPLE. 



shewn in the case of the skin by puncturing any 

 part of it with a needle. The total quantity is 

 estimated at about one-eighth of the weight of the 

 body, or about 20 Ibs. in a man of average size. Its 

 colour is red, but it varies from a bright scarlet in 

 the arteries to a dark purple in the veins. When, 

 however, a minute drop is examined under the 

 microscope, it is seen to be made up of, first, 

 a clear colourless fluid; and, secondly, of a 

 multitude of small solid bodies or corpuscles, 

 which float in the plasma. This plasma, called 

 liquor sanguinis, is composed of water richly 

 charged with materials derived (through the 

 chyme) from the food ; namely, albumen, fibrine, 

 various fats, &c. The greater part of the blood 

 about 70 per cent. is made up of water. It con- 

 tains a very small amount of fibrine, about 7 per 

 cent, of albumen, 14 per cent, of corpuscles, and 

 the remainder consists of extractive matters, fats, 

 and various salts. The great majority of the cor- 

 puscles are of a yellowish-red colour, and by their 

 enormous number seem to impart a red hue to the 

 blood ; while a few are white or colourless. The red 

 coruscles have a diameter of about ^sWth of an 



Fig. 2. Blood Corpuscles 

 highly magnified. 



inch, being about th of that fraction in thickness ; 

 and in form they are circular biconcave discs, and 

 in freshly drawn blood they arrange themselves 

 by contact of their flat surfaces into little rolls 

 like piles of coins. The colourless corpuscles 

 are larger, globular in form, and present a 

 granulated appearance. 

 Recently it has been 

 shewn that these are 

 little masses of living 

 protoplasm, capable of 

 spontaneous movement, 

 and that they are iden- 

 tical with the corpuscles 

 found in purulent matter 

 or pus. In all classes 

 of animals the colour- 

 less corpuscles are alike ; 

 but the form of the 

 coloured corpuscles varies, being oval in fishes, 

 reptiles, and birds. In all mammals they are 

 circular, with the exception of the camels and 

 llamas, where they are oval. Shortly after its 

 removal from the body, the blood begins to thicken 

 or coagulate, and soon separates into two distinct 

 parts, one of them being a dark-red jelly or clot, 

 which is the heavier of the two, and sinks ; while 

 the other is a clear straw-coloured fluid, called the 

 serum, which covers the clot. This depends on the 

 formation of a substance called fibrine, which forms 

 a meshwork of fine molecular fibres, entangling 

 the corpuscles. When a coagulum appears, 

 fibrine is produced by the union of two sub- 

 stances present in solution, one called fibrino- 

 gen, and the other termed fibrino-plastic sub- 

 stance, the latter probably being a substance 

 known as globulin, which forms a large part of 

 the coloured corpuscles. This remarkable prop- 

 erty of coagulation is the chief cause of the arrest 

 of bleeding from a wound. 



The blood is in constant motion in a definite 

 direction during life, and the motion is known as 

 the circulation. Its true course was discovered 

 by Harvey, about 1620. The organs of circulation 

 are the heart, arteries, veins, and capillaries. The 

 course of the blood through these organs will be 

 best elucidated by the aid of a diagram, which 



118 



left auricle ; a, aorta ; d, 

 vena cava ; e, greater circula- 

 tion ; b, smaller circulation ; 

 f, pulmonary artery ; g, pul- 

 monary veins. 



is equally applicable for all other mammals as well 

 as for man and for birds. The shaded part of fig. 3. 

 represents structures filled with impure or venous- 

 blood, while the unshaded 

 portion represents struc- 

 tures in which pure oxy- 

 genated arterial blood oc- 

 curs. In this diagram 

 we observe a dotted 

 circle, representing a 

 closed bag or sac, termed 

 the pericardium, and in- 

 closing the four cavities 

 c, v, c', v', of which the 

 heart is composed. Two 

 of these cavities, c and </, 

 are for the purpose of re- 

 ceiving the blood as it 

 flows into the heart, and 

 are termed the auricles ; 

 while the two cavities, v 

 and v' y are for the purpose 

 of propelling the blood Fig. 3. Mode of Circula- 

 through the lungs and tion in Man and other 

 general system respec- Mammals, and in Birds : 

 lively, and are termed the h > heart ; . "g ht ventricle ; T/, 

 ventricles. The vessels 

 that transport blood into 

 the auricles are termed 

 veins ; and the vessels 

 through which blood is 

 driven onwards from the ventricles are known as 

 arteries. The diagram further shews that what we 

 commonly term the heart is in reality two distinct 

 hearts in apposition with each other ; one, shaded 

 in the figure, which is called the right, or venous, or 

 pulmonary heart ; and the other, unshaded, which 

 is called the left, or arterial, or systemic heart, the 

 last name having been given to it because the 

 blood is sent from it to the general system ; just 

 as the right heart is termed pulmonary from its 

 sending blood to the lungs. We will now trace 

 the course of the blood as indicated by the arrows 

 in this diagram, commencing with the right 

 auricle, c. The right auricle contracting upon the 

 venous or impure blood which has been returned 

 from the body, and with which we suppose it to be 

 filled, drives its contents onwards into the right 

 ventricle, v, through an opening between these 

 two cavities, called the right auriculo-ventricular 

 opening, which is guarded by a valve, named 

 tricuspid, from its being composed of three 

 pointed membranous expansions, which almost 

 entirely prevents the regurgitation or reflux of the 

 blood from the ventricle into the auricle. The 

 ventricle, v, being now filled, contracts ; and, as 

 the blood cannot return into the auricle, it is 

 driven along the shaded vessel, the dividing 

 branches of which are indicated by f. This 

 vessel is known as the pulmonary artery, and 

 conveys the blood to the lungs. At its commence- 

 ment it is guarded by valves, termed, from their 

 shape, the semilunar pulmonary valves, which 

 entirely prevent the blood which has once been 

 propelled into the pulmonary artery from re- 

 entering the ventricle. The pulmonary artery 

 gradually divides into smaller and smaller branches,, 

 which ultimately merge into capillaries. In these 

 capillaries, which are freely distributed over the 

 external surface of all the air-cells (of which the 

 lung is mainly composed), the venous blood is 



