HUMAN PHYSIOLOGY. 



61 



oolla, composed of a delioato colourless membrano enclosing 

 a. ooloarod substance which appears to be uniform in composition, 

 !i:ivii!ff no nucleus. Others believe them to bo solid masses 

 " lump* of nutriment " having no cell-wall. In size they vary 

 lie xJn to ^K, of an inch in diameter. Their presence 

 is character MI Vortobrata, aa they do not occur in 



the blood of any animals not included in that division. Their 

 proportion to the white seems to vary according to the degree of 

 Miiisation of the animal. Thus, in man and the higher 

 ..nun. i!s, they are from 20 to 300 times aa numerous; in tho 

 fish and reptile they are comparatively few in number, though 

 even horo they always exceed the white. Those of the class 

 Mammalia differ from those of the fish and bird in having no 

 nuclei, and also in shape, the latter being, as a rule, oval or 

 flliptiral. Tho mammals also differ in some degree in size from 

 each other ; and upon those differences it has occasionally been 

 attempted to base a judgment as to the particular animal from 

 which the blood was derived ; but though by tho aid of the micro- 

 scope it is possible to say, with some certainty, as to whether 

 the blood is that of a mammal, or that of a bird or fish, this 

 appears to be the limit ; tho differences in the size of the 

 corpuscles are neither sufficiently great nor constant to decide 

 positively whether they are those of a man, a pig, or a cow. 



The white corpuscle is larger than tho red, being about jjg of 

 an inch in diameter, and is spherical in shape ; they have a 

 tnbercnlatod surface, and are of a greyish-pearly appearance ; 

 they are made up of a cell-wall, enclosing a white-looking sub- 

 stance, which has one or more nuclei. The 

 serum of the blood, the liquid which remains 

 after the coagulation of the fibrine, is an 

 alkaline, slimy, viscid fluid of a yellowish or 

 greenish colour. It consists of a large number 

 of substances dissolved in water ; its largest 

 solid constituent is albumen, which is present 

 to the extent of about 8 per cent. The pre- 

 sence of this element may be made manifest 

 by heating the serum, when the albumen 

 coagulates into a solid mass. Tho liquid 

 which remains nncoagulated is called the 

 serosity. When meat is cooked for eating, 

 the serum of the blood is converted into solid 

 ilbumen, and this, when cut, allows the 

 serosity to escape in the shape of gravy. 



Such, then, being the principal parts of 

 the blood, we must now examine a little its 

 chemical composition. For this purpose two 

 tables are given, the first showing in slight 

 detail the various chemical substances found in the blood, and 

 the ether the proportion of its ultimate elements. 



TABLE I. 



SHOWING THE PROPORTIONS OP THE PRINCIPAL CONSTITUENTS IS A 

 THOUSAND PARTS OF BLOOD. 



Water 784 



Albumen ....... 70 



THE ORGANS OP CIRCTTLATIOH. 



and 



Bed Corpuscles I Hmato-crystalline 

 I Haematine . . 



Fibrine 



123-5 

 7'3 

 Fatty Matter 



ide of Sodium 3 '6 



id Phosphate of Iroa '5 

 Salts . . . 1-93 

 Extractive Matters, Biliary Colouring Matters, 

 Oases, etc. 



Salts 



f Chloride i 

 < Oxide anc 

 I Other Sal 



2-2 

 131 

 1-3 



6-03 



5-47 



TABLE II. 

 SHOWING THE ULTIMATE ELEMENTS OF DRIED BLOOD. 



Carbon 57 D percent. 



Hydrogen . . 7'1 



Nitrogen 17'4 



Oxygen 19'2 



Ashes 4-4 



In tho serum is contained a great part of the salts, the 

 albumen, and the water of the blood. The proportion of the 

 latter element varies, and is influenced by many causes. Thus 

 all active exercises which produce perspiration diminish the 

 quantity of the water in the blood ; but as they, at the same time, 

 create thirst, a larger quantity of liquid is taken, and so the 

 Valanon is restored. Water is truly one of the most important 



elements, because upon its pretence in proper proportion* 

 depends the maintenance of tho due viscidity of the blood, and 

 the power to absorb the nutritive element* from the digested 

 food. The fibrino is a Tory important substance, and in health 

 is present to the amount of 2 to 3 parts in 1,000 ; but in all 

 diseases of a low type it i diminished, and in some of the 

 opposite character it is increased. The red corpuscles consist, 

 as is indicated in Table I., of two distinct constituents : the one 

 called crystalline or globuline, which forms the balk of the 

 whole, is one of the albuminous group of substances ; the other, 

 called hiematine, is distinguished from all other animal sub- 

 stances by its peculiar red colour, and the large proportion of 

 iron which it contains. The fatty matters vary much in quan- 

 tity, being increased soon after a meal a taken if it contains 

 fatty, starchy, or saccharine substances. 



As has been already stated, the sources from which the blood 

 is renewed are the chyle and lymph, which are poured into the 

 circulation by the thoracic duct. The lymph and chyle corpuscles 

 are probably identical with the white corpuscles of the blood, 

 and the red is believed to be formed from the white the cell- 

 wall becoming gradually smooth and the nuclei vanishing, 

 whilst the whole cell assumes the red colour of the completed 

 corpuscle. The fibrine makes its appearance in the chyle almost 

 coincidently with the corpuscles, but does not appear to have its 

 full power of coagulating till it reaches the completed blood. 

 Wo pass on now to consider the second division of this function 

 of circulation, the organs by which it is carried out ; these are 

 the heart and thj blood-vessels, consisting of 

 arteries, capillaries, and veins. 



The heart is a hollow muscular organ of a 

 conical form, placed between the two lungs, 

 and enclosed in the pericardium ; its posi- 

 tion in the chest is oblique ; its broad end or 

 base, which is placed highest in the chest, is 

 directed upwards and backwards to the right, 

 the point or apex is directed forwards and to 

 the left side ; the heart is placed between the 

 lower two-thirds of the sternum, and projects 

 more to the left than it does to the right, 

 extending about three inches from the median 

 line in tho former direction, and only an inch 

 and a half in the latter. Anteriorly, it is 

 rounded and convex, whilst its posterior sur- 

 face is flattened and rests on the diaphragm. 

 Its ordinary size in the adult is about five 

 inches in length, three inches and a half in 

 breadth at its broadest part, and two inches 

 half in thickness ; its weight is from ten to twelve 

 ounces in men, and from eight to ten in women ; it con- 

 tinues to increase in size up to an advanced period in life. 

 The pericardium in which the heart is enclosed is one of 

 the serous membranes, and is consequently a closed sac con- 

 sisting of two layers, between which is a small quantity of 

 fluid, to enable the surfaces to glide easily over each other ; 

 the pericardium at its lower surface is firmly attached 

 to the diaphragm, and serves to support the heart in its 

 place, and facilitates its various movements. When the heart 

 is laid open, it is seen that it is composed of four chambers, 

 divided into a right and left set by a longitudinal muscular 

 septum which runs the whole length of the organ, so that 

 the right set is completely cut off from those of the opposite 

 side. The upper pair of these cavities are called the auricles ; 

 the lower pair the ventricles. The auricles, which are much 

 smaller than the ventricles, are the chambers which receive the 

 blood ; into the right ones open tho large veins which bring the 

 used blood back to the heart from all parts of the body ; into the 

 left, the pulmonary veins, which convey the blood after it has 

 passed through the lungs. The ventricles are the chambers 

 which by their contraction drive the blood out, the right sending 

 the blood which it receives from the right auricle into the pul- 

 monary artery, to be by it conveyed to the lungs, and there 

 exposed to tho action of the air ; the left pumping the aerated 

 blood sent into it by its auricle into the great blood-vessel, the 

 aorta, to be distributed to all parts of the body. The inside of 

 the heart is, like the outside, covered by a serous membrane in 

 this instance called the endocardium, which, by its thin smooth 

 transparency, gives to the inside of the heart its glistening 

 appearance ; this membrane, at the various apertures in the 



