The location of the heart in the thoracic cavity causes movements of the chest walls to draw blood into the right auricle for the same reason that they "draw" air into the lungs.
Active exercise through short intervals, followed by periods of rest, such as the exercise furnished by climbing stairs, or by short runs, is considered the best means of strengthening the heart.
Nosebleed in connection with any kind of severe sickness should receive prompt attention, since a considerable loss of blood when the body is already weak may seriously delay recovery.
Newton, Practical Hygiene.
On account of its position in the body, the lymph is not easily collected for examination. Still, nearly every one will recall some experience that has enabled him to see lymph. The liquid in a water blister is lymph, and so also is the liquid which oozes from the skin when it is scraped or slightly scratched. Swelling in any part of the body is due to the accumulation of lymph at that place.
In certain small animals of the lowest types a single liquid, serving as a medium of exchange between the cells and the body surface, supplies all the needs of the organism. In larger animals, however, where materials have to be moved from one part of the cell group to another, a portion of the nutrient fluid is used for purposes of transportation. This is confined in channels where it is set in motion by suitable organs. The portion which remains outside of the channels then transfers material between the cells, on the one hand, and the moving liquid, on the other.
Surgeons in opening veins near the thoracic cavity have to be on their guard to prevent air from being sucked into them, thereby causing death.
Oxygen forms about 21 per cent of the atmosphere, nitrogen about 78 per cent, carbon dioxide about .03 per cent, and the recently discovered element argon about 1 per cent. The oxygen is in a free, or uncombined, condition—the form in which it can be used in the body.
The peculiar work devolving upon the organs of respiration necessitates a special plan of construction—one adapted to the properties of the atmosphere. Being concerned in the movement of air, a gaseous substance, they will naturally have a structure different from the organs of circulation which move a liquid (the blood). All the organs of the body are adapted by their structure to the work which they perform.
In ordinary inspirations the force that causes the air to move through the passages is scarcely an ounce to the square inch, while in forced inspirations it does not exceed half a pound. On this account the closing of any of the air passages by pressure, or by the presence of foreign substances, would keep the air from reaching some part of the lungs.