between the inanimate and the animate, that is, between plants and animals, is no less decided: for, of the two sets of actions which have been enumerated, the one, as has just been stated, is common to the whole class of living beings, while the second set is peculiar to one division of that class. The plant performs only the organic actions: all the vital phenomena it exhibits are included in this single circle; it is, therefore, said to possess only organic life: but the animal performs both organic and animal actions, and is therefore said to possess both organic and animal life. Both the organic and the animal actions are accomplished by means of certain instruments, that is, organized bodies which possess a definite structure, and which are moulded into a peculiar form. Such an instrument is called an organ, and the action of an organ is called its function. The leaf of the plant is an organ, and the conversion of sap by the leaf into the proper juice of the plant, by the process called respiration, is the function of this organ. The liver of the animal is an organ; and the conversion of the blood that circulates through it into bile, by the process of secretion, is its function. The brain is an organ; the sentient nerve in communication with it is also an organ. The extremity of the sentient nerve receives an impression from an external object, and conveys it to the brain, where it becomes a sensation. The transmission of the impression is the function of the nerve; the conversion of the impression into a sensation is the function of the brain. The living body consists of a congeries of these instruments or organs: the constituent matter of these organs is always partly in a fluid and partly in a solid state. Of the fluids and solids which thus invariably enter in combination into the composition of the organs, the fluids may be regarded as the primary and essential elements, for they are the source and the support of the solids. There is no solid which is not formed out of a fluid; no solid which does not always contain, as a constituent part of it, some fluid, and none which is capable of maintaining its integrity without a continual supply of fluids.