Physiology and Hygiene for Secondary Schools

the blood and the cells. The central tube is a capillary. The

es themselves. The capillaries, to be sure, bring the blood very near the cells of the different tissues; still, there is need of a liquid to fill the space between the capillaries and the cells

gle layer of flat cells placed edge to edge. Partly on account of the pressure upon the blood and partly on account of the natural tendency of li

hese mix with the plasma from the blood, forming the resultant liquid which is the lymph. A considerable amount of the ma

nt constituents of the blood are found in the lymph, but in different proportions. Food materials for the cells are present in smaller amounts than in the blood, while impuritie

es, but it coagulates more slowly than does the blood. The most noticeable difference between these liquids is that of color, the lymph being

the one[pg 067] hand, and with certain blood vessels on the other, is a system of tubes that return the lymph to the blood stream. The smallest of these, and the ones in greatest abundance, are called lympha

ft subclavian vein. 4. Right subclavian vein. 5. Superior vena cava. 6. Lacteals. 7. Lymphatic gla

led the right lymphatic duct, receives the lymph from the lymphatics in the right arm, the right side of the head, and the region of the right shou

the subclavian vein on the upper side at the place where it is joined by the left jugular vein. The thoracic duct has a length of from sixteen to eighteen inches, and is about as large around as a goose quill. The lower end t

cteals (Fig. 28). These do not differ in structure from the lymphatics in other parts

e in length. The lymph vessels generally open into them on one side and leave them on the other (Figs. 28 and 30). They are not glands in function, but are so called because of their having the general form of

s the blood to minister to the[pg 069] needs of the cells. But the lymph and the blood, everything considered, can hardly be looked upon as two separate and distinct liquids. Not only do they supplement each other in their work and possess striking similarities, but each is made in its movements to pass

quid. But, as already suggested, it has certain movements which are necessary to the purpos

m the capillaries

m the cells towar

ymph spaces into the lymphatics and along these chan

second and third movements the lymph, more or less laden with im

rt, is known to be connected with these tubes and[pg 070] to supply the pressure necessary for moving the lymph.

rt makes room for itself by pushing a portion of the lymph out of the lymph spaces. This in turn presses upon the lym

close them up and to push the lymph past the valves, which, by closing, prevent its return (Fig. 29). Pressure at the surface of the body

mph. A. Relaxed muscle beside which is a lympha

ic space. This not only causes the air to flow into the lungs (Chapter VII), but also causes a movement of the blood and lymph in such of their tubes as enter thi

pressure is less than the pressure that moves the lymph. Such a place is found in the thoracic cavity. As already pointed out (page 54), the blood pressure in the veins entering this cavity becomes, with each expansion of the chest, negative, i.e., less than the pressure of the atmosphere on the outside of the body. This, as we have seen, aids in the flow of the blood into the right auricle. It also aids in the passage of lymph into the blood vessels. The ly

place of relatively high pressure at the lymph spaces to

derstood. Blood pressure in the capillaries undoubtedly has much to do in forcing the plasma through the capillary walls, but this tends to prevent the movement of the l

right membranous partitio

e with pure water and on the other with water containing salt, an exchange of materials will take place through the membrane until the same proportion of salt exists on the two sides (Fig. 31). Th

be shown by suitable experiments (see Practical W

iquids to the same condition, a difference in density causes the flow to be greater from the less dense toward the denser liquid, than in the opposite d

ing, the partition. If but one of the liquids penetrat

ides of the partition must

ygen and food materials, which are found in great abundance in the blood, are less abundant in the lymph and still less abundant in the cells. According to the principle of osmosis, the main flow of oxygen and food is from the cap

tions. The chief point of interest about substances in solution is that they are very finely divided and that their little particles are free to move about in the liquid that contains them. Both the motion and th

embrane which surrounds it. Examples of crystalloids are found in solutions of salt and sugar in water. The inability of a colloid to penetrate a membrane is due to the fact that it does not form a true solution. Its particles (molecules), instead of being completely separated, still cling together, forming little masses tha

partitions of the body. An example of such is found in the proteids of the blood which, as a colloidal solution, pass through the capillary walls to become a part of the lymph. Perhaps[pg 074] the best explanation offered as

he system for the circulation of the blood. By adding new material to the lymph and withdrawing waste material from it, the blood keeps this liquid in a suitable condition for supplying the needs of the cells. Supplementing each other in

n the necessity for

h reference to density, color,

reference to color, compositio

re in the capillaries ca

mph to move. Compare with the effect of musc

ight hand to where it enters the blood; f

a movement of food and oxygen in one direction

ater play in the ex

together fulfill all the requirements

g

TICA

in a tumbler on a table. In this position quickly inhale air through the nostrils, noting that with each inhalation there is a slight movement of the wate

and then picked off with a pair of forceps, or a small knife blade. Fit a small glass tube, eight or ten inches long, into the other end so that it will penetrate the membrane and pass down into the yolk. Securely fasten t

ch as sugar, salt, or copper sulphate. Suspend in a vessel of water so that the liquid which it contains is just on a level with the water in the vessel. Examine from time to time, looking for evidence of a movement in each direction through the membrane. Why should th

-An osm

of osmosis may be more easily illustrated than by the method in either of the

g