A Text Book of Physiology V 1 1893

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: setting free energy so as to move itself, and by reason of its sensitiveness so directing that energy as to produce a movement suitable to the conditions of its surroundings, has at the same time to bear the labour of taking in raw food, of selecting that part of the raw food which is useful and rejecting...
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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: setting free energy so as to move itself, and by reason of its sensitiveness so directing that energy as to produce a movement suitable to the conditions of its surroundings, has at the same time to bear the labour of taking in raw food, of selecting that part of the raw food which is useful and rejecting that which is useless, and of working up the accepted part through a variety of stages into its own living substance; that is to say, it has at the same time that it is feeling and moving to carry on the work of digesting and assimilating. It has moreover at the same time to throw out the waste matters arising from the changes taking place in its own substance, having first brought these waste matters into a condition suitable for being thrown out. 8. In the body of man, movements, as we shall see, are broadly speaking carried out by means of muscular tissue, and the changes in muscular tissue which lead to the setting free of energy in the form of movement are directed, governed, and adapted to the surroundings of man, by means of nervous tissue. Rays of light fall on the nervous substance of the eye called the retina, and set up in the retina changes which induce in the optic nerve other changes, which in turn are propagated to the brain as nervous impulses, both the excitation and the propagation involving an expenditure of energy. These nervous impulses reaching the brain may induce other nervous impulses which travelling down certain nerves to certain muscles may lead to changes in those muscles by which they suddenly grow short and pull upon the bones or other structures to which they are attached, in which case we say the man starts; or the nervous impulses reaching the brain may produce some other effects. Similarly, sound falling on the ear, or contact between the ...