246. But while, in this process, some of the vessels of the clot can be distinctly traced from the surrounding living parts, others appear to have no communication with those parts, at all events no such communication can be traced. These vessels, the origin of which cannot be found external to the clot, are supposed by some physiologists to be formed within it. Within the living egg, during incubation, certain motions or actions are observed spontaneously to arise, which terminate in the development of the chick. Analogous motions arising within the clot terminate, it is conceived, in the development of blood-vessels. According to this view, a simultaneous action takes place in the clot, and in the living part with which it is in contact; each shooting out vessels which elongate, approximate, unite, and thus establish a direct vital communication. Whether this view of the process of organization be the correct one or not does not affect the present argument. It is certain that a clot of blood surrounded by living parts becomes organized; it is certain that no dead substance surrounded by living parts becomes organized; it follows that the blood possesses life.
247. Health and life depend on the quantity, quality, and distribution of the blood. The chief source from which the blood itself is derived is the chyle: hence too much or too little food, or too great or too little activity of the organs that digest it, may render the quantity of the blood preternaturally abundant or deficient; or though there be neither excess nor deficiency in the quantity of nourishment formed, parts of the blood which ought to be removed may be retained, or parts which ought to be retained may be removed, and hence the actual quantity in the system may be superabundant or insufficient.
248. The relative proportion of every constituent of the blood is capable of varying; and of course in the degree in which the healthy proportion is deranged, the quality of the mass must undergo a corresponding deterioration. The watery portion is sometimes so deficient, that the mass is obviously thickened; while at other times the fluid preponderates so much over the solid constituents, that the blood is thin and watery. The albumen, the quantity of which varies considerably even in health, in disease is sometimes twice as great, and at other times is less than half its natural proportion. In some cases the fibrin preponderates so much, that the coagulum formed by the blood is exceedingly coherent, firm and dense; in other cases the quantity of fibrin is so small, that the coagulation is imperfect, forming only a soft, loose and tender coagulum, and in extreme cases the blood remains wholly fluid. When the vital energy of the system is great, the red particles abound; when it is depressed, they are deficient. In the former state, they are of a bright red colour; in the latter, dusky, purple, or even black. When the depression of the vital energy is extreme, the power of mutual repulsion exerted by the particles would seem to be so far destroyed as to admit of their adhering to each other partially in certain organs; while in other cases they seem to be actually disorganised, and to have their structures so broken up, that they escape from the current of the circulation as if dissolved in the serum, through the minute vessels intended only for the exhalation of the watery part of the blood. This fearful change is conceived to have an intimate connexion with a diminution of the proportion of the saline constituents. Out of the body, as has been shown, the red particles change their figure instantaneously, and are rapidly dissolved when in contact with pure water; while they undergo little change of form if the water hold saline matter in solution. It would seem that one use of the saline constituents of the blood is to preserve entire the figure and constitution of the red particles. It is certain that any change in the proportion of the saline constituents produces a most powerful effect on the condition of the red particles. It is no less certain that changes do take place in the proportion of the saline constituents. In the state of health, the taste of the blood is distinctly salt, depending chiefly on the quantity of muriate of soda contained in it. In certain violent and malignant diseases, such, for example, as the malignant forms of fever, and more especially that form of it termed pestilential cholera, this salt taste is scarcely, if at all, perceptible; and it is ascertained that, in such cases, the proportion of saline matter is sensibly diminished.
249. The quality of the blood may be also essentially changed by the disturbance of the balance of certain organic functions: digestion, absorption, circulation, respiration, are indispensable to the formation of the blood and to the nourishment of the tissues. Absorption, nutrition, secretion, circulation, render the blood impure, either by directly communicating to it hurtful ingredients, or by allowing noxious matters to accumulate in it, or by destroying the relative proportion of its constituents. Organs are specially provided, the main function of which is to separate and remove from the blood these injurious substances. Organs of this class are called depurating, and the process they carry on is denominated that of depuration. The lungs, the liver, the kidneys, are depurating organs, and one result at least of the functions they perform is the purification or depuration of the blood. If the lung fail to eliminate carbon, the liver bile, the kidney urine, carbon, bile, urine, or at least the constituents of which these substances are composed, must accumulate in the blood, contaminate it, and render it incapable of duly nourishing and stimulating the organs.
250. But though the blood be good in quality and just in quantity, health and life must still depend upon its proper distribution. It may be sent out to the system too rapidly or too slowly. It may be distributed to different portions of the system unequally; too much may be sent to one organ, and too little to another: consequently, while the latter languishes, the former may be oppressed, overwhelmed or stimulated to violent and destructive action. In either case health is disturbed and life endangered.
251. Of the mode and degree in which food, air, moisture, temperature, repletion, abstinence, exercise, indolence, influence the quantity, quality, and distribution of the blood; of the mode in which the condition of the blood modifies the actions both of the organic and the animal organs; of the reason why health and disease are wholly dependent on those states and actions, a clear and just conception may be formed when the several functions have been described, and the precise office of each is understood.
[CHAPTER VII.]
OF THE CIRCULATION.
Vessels connected with the heart: chambers of the heart—Position of the heart—Pulmonic circle: systemic circle—Structure of the heart, artery, and vein—Consequences of the discovery of the circulation to the discoverer—Action of the heart: sounds occasioned by its different movements—Contraction: dilatation—Disposition and action of the valves—Powers that move the blood—Force of the heart—Action of the arterial tubes: the pulse: action of the capillaries: action of the veins—Self-moving power of the blood—Vital endowment of the capillaries: functions—Practical applications.