THE MECHANISM OF LIFE 



CHAPTER I 

 '^ ON THE NATURE OF ANIMAL LIFE 



The Organism as a Structure. — The student of biology 

 usually begins his studies by dissecting the body of a warm- 

 blooded animal; and, first of all, he notices a division of this 

 into well-marked regions: head and neck, trunk, limbs, and 

 perhaps a tail. Then, taking a knife, he slits the skin over a 

 limb and finds beneath it fleshy masses (the muscles) attached 

 to rigid supports (the bones). He sees that the latter are 

 movable on each other by articulations, or joints, and from his 

 general knowledge of the animal in the living state he recognises 

 that bones and muscles are parts that move in ways that depend 

 on the nature of the articulations. Looking more closely, he 

 sees white, gUstening threads beginning in the muscles, joining 

 together and passing into the central parts of the body. These 

 are the nerves. There are also two kinds of bloodvessels: 

 one kind which are stiff and white and apparently empty, and 

 another kind which are rather thicker and softer, and which 

 contain blood. The former are arteries, and the latter veins. 

 All these parts — bones, muscles, nerves, arteries and veins — are 

 wrapped up in a loose kind of material called connective tissue, 

 and this must always be separated in order to disclose the forms 

 of the muscles and other parts, and the ways in which they are 

 joined together. 



Then, opening the cavities of the body, he discovers the viscera 

 — that is, the lungs and heart, which occupy the cavity of the 

 thoracic region of the trunk and the stomach, fiver, alimentary 

 canal, kidneys, digestive glands, and reproductive organs, all 

 of which are contained in the abdominal cavity. Here, too, 

 attentive study shows the existence of bloodvessels and nerves 

 which ramify among the visceral parts. 



Lastly, breaking open the bones of the skull, he finds a white, 



