Animal Life and Intelligence Author:C. Lloyd Morgan Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: gation into tissues and organs, it remains true that the body of one of the higher animals is composed of cells, together with certain cell-products, horny, calc... more »areous, or other. The simplest animals, called protozoa, are, however, unicellular, each organism being constituted by a single cell. We must notice that, even during periods of apparent inactivity — for example, during sleep — many life-processes are still in activity, though the vigour of action may be somewhat reduced. When we are fast asleep, respiration, the heart-beat, and the onward propulsion of food through the alimentary canal, are still going on. Even at rest, the living animal is a going machine. In some cases, however, as during the hibernating sleep of the dormouse or the bear, the vital activities fall to the lowest possible ebb. Moreover, in some cases, the life-processes may be temporarily arrested, but again taken up when the special conditions giving rise to the temporary arrest are removed. Frogs, for example, have been frozen, but have resumed their life-activities when subsequently thawed. Let us take the function of respiration as a starting- point in further exemplification of the nature of the life-processes of animals. The organs of respiration, in ourselves and all the mammalia, are the lungs, which lie in the thoracic cavity of the chest, the walls of which are bounded by the ribs and breast-bone, its floor being formed of a muscular and movable partition, the diaphragm, which separates it from the stomach and other alimentary viscera in the abdominal region. The lungs fit closely, on either side of the heart, in this thoracic cavity ; and when the size of this cavity is altered by movements of the ribs and diaphragm, air ia either sucked into or expelled from the lungs through the wind...« less