ITS STRUCTURE AND FUNCTIONS (ANATOMY AND PHYSIOLOGY).
The lungs are the organs of respiration, that is, of breathing. Everyone knows that the con tinuance of the acts of breathing is necessary to life, and that if respiration be suspended, as it is in choking, strangling, drowning, &c., for even a few minutes, death results. The vast importance of this bodily function, and the great and constant danger of any disease that seriously interferes with its due performance, will be fully appreciated if a general statement of the position it holds in the processes of life be here given by way of introduction to this section.
At the beginning of Section XIV it is stated that a particular order has been followed in the consideration of the various organs of the body, so that any one who chooses to read the sections dealing with structure and functions, one after another in their order, may have a general idea of the whole living human machine.
Section X. discusses the means by which food is prepared to form part of a nourishing fluid —the blood,—and also describes other sources of blood - forming material. Section XIV. follows out the same line by describing the nature of the blood and the means by which it is distributed throughout the body. It points out also (p. 296) that the purpose of the blood is to nourish each minutest element of the body, to give to it raw material for its use in growth and activity, and that it not only gives up to tissues something to maintain them, but acts as a means of carrying away from them the products of their activity, waste substances which, if allowed to remain, would impair their health and vigour, and that thus the blood becomes impoverished as much by poisonous materials added to it as by nourishing materials taken from it.
Now the sources of new nourishment to the blood are all carefully considered in Sections X. and XII., with one exception, that of oxy gen gas; but none of the means by which poisonous waste matters cast into the blood are removed has yet been considered.
The lungs supply the oxygen, and on this ground must be considered as organs of blood formation. But at the same time that they sup ply oxygen, and by the same method, they re move from the blood carbonic acid gas, and that gas is one of the principal waste substances. On this ground, therefore, they rank as blood puri fiers. If, then, the lungs are seriously interfered with, a twofold blow is dealt at the blood—the very stream of life,—for the risk at once arises