HANDBOOK OF PHYSIOLOGY 



CHAPTER I. 



THE PHENOMENA OF LIFE. 



HUMAN Physiology is the science which treats of the various pro- 

 cesses or changes which take place during life in the organs and tissues 

 of the body of man. These processes, however, must not be considered 

 as by any means peculiar to the human organism since, putting aside 

 the properties which serve to distinguish man from other animals, as 

 well as those which mark out one animal from another, the changes 

 which go on in the tissues of man go on much in the same way in the 

 tissues of all other animals as long as they live. Furthermore it is 

 found that similar changes proceed in all living vegetable tissues; they 

 indeed constitute what are called vital phenomena, and are those proper- 

 ties which mark out living from non-living material. 



The lowest types of life, whether animal or vegetable, are found to 

 consist of minute masses of a jelly-like substance, which is now gener- 

 ally known under the name of protoplasm. Each such minute mass is 

 called a cell, so that these minute elementary organisms are designated 

 unicellular. Not only is it true that the lowest types of life are made 

 up of protoplasm, but it has also been shown that the tissues of which 

 the most complex organisms are composed consist of protoplasmic cells. 



Thus, for example, the human body can be shown by dissection to 

 be constructed of various dissimilar parts, bones, muscles, brain, heart, 

 lungs, intestines, etc., and these on more minute examination with the 

 aid of the microscope, are found to be composed of different tissues, 

 such as epithelial, connective, nervous, muscular, and the like. Each of 

 these tissues is made up of cells or of their altered equivalents. Again, 

 we are taught by Embryology, the science which treats of the growth 

 and structure of organisms from their first coming into being, that the 

 human body, made up of all these dissimilar structures, commenced its 

 life as a minute cell or ovum (fig. 2) about T^th of an inch in diame- 

 ter, consisting of a spherical mass of protoplasm in the midst of which 

 was contained a smaller spherical body, the nucleus or germinal vesicle. 



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