If the blood be stirred or "whipped" while it is coagulating, the clot may be broken up and the fibrin separated as fast as it forms. The blood which then remains consists of serum and corpuscles and will not coagulate. It is known as "defibrinated" blood.
Certain substances, called opsonins, have recently been shown to exist in the plasma, that aid the white corpuscles in their work of destroying germs. The opsonins appear to act in such a manner as to weaken the germs and make them more susceptible to the attacks of the white corpuscles.
Some of the changes in the blood are very closely related to our everyday habits and inclinations. For example, a lack of nourishment in the blood causes hunger and this leads to the taking of food. If the fluids of the body become too dense, a feeling of thirst is aroused which prompts one to drink water.
Metchnikoff, The New Hygiene.
A physiological salt solution is prepared by dissolving .6 of a gram of common salt in 100 cc. of distilled water or pure cistern water. This solution, having the same density as the plasma of the blood, does not act injuriously upon the corpuscles.
The term "circulation" literally means moving in a circle. While the blood does not move through the body in a circle, the term is justified by the fact that the blood flows out continually from a single point, the heart, and to this point is continually returning.
The heart at first glance seems to bear little resemblance to the pumps in common use. When it is remembered, however, that any contrivance which moves a fluid by varying the size of a cavity is a pump, it is seen that not only the heart, but the chest in breathing and also the mouth in sucking a liquid through a tube, are pumps in principle. The ordinary syringe bulb illustrates the class of pumps to which the heart belongs. (See Practical Work.)
The contraction of the heart is known as the systole and its relaxation as the diastole. The systole plus the diastole forms the so-called "cardiac cycle" (Fig. 18). This consists of (1) the contraction of the auricles, (2) the contraction of the ventricles, and (3) the period of rest. The heart systole includes the contraction of both the auricles and the ventricles.
Martin, The Human Body.
The pressure maintained by the left ventricle has been estimated to be nearly three and one half pounds to the square inch—a pressure sufficient to sustain a column of water eight feet high. The pressure maintained by the right ventricle is about one third as great. In maintaining this pressure the heart does a work equal to about one two-hundredth of a horse power.