HANDBOOK OF PHYSIOLOGY 



CHAPTER I 

 THE PHENOMENA OF LIFE 



PHYSIOLOGY is the science which treats of the various processes or changes 

 which take place in the organs and tissues of the body during life. These 

 processes, however, must not be considered as by any means peculiar to the 

 human organism, since, putting aside the properties which serve to distin- 

 guish man from other animals, the changes which go on in the tissues of man 

 go on in much 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 properties which mark out living from non-living material. 



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

 sist of minute masses of a substance generally known under the name of 

 protoplasm. Each such living mass is called a cell, so that these minute 

 elementary organisms are designated unicellular. 



The phenomena of life are exhibited by protoplasm, whether that exists 

 in the simple form typified by a microscopic one-celled animal, or in a more 

 complex mass represented by the organs and tissues of animals and plants. 

 In the lowest type of life the morphological unit of structural organization is 

 represented by the single cell. In the more complex organisms of both ani- 

 mals and plants the total mass represents a great aggregation of more or less 

 distinct cells. A degree of differentiation takes place whereby the tissues 

 and organs of the body of plants and animals present great aggregates of 

 differentiating cells. It must be at once evident that the great mass of knowl- 

 edge dealing with the nature and activities of protoplasm constitutes the 

 science of physiology. The cell, therefore, is the working unit in physiology 

 no less than in morphology. 



The prime importance of the cell as an element of structure was first 

 established by the researches of the botanist Schleiden, and his conclusions, 

 drawn from the study of vegetable histology, were at once extended by Theo- 

 dor Schwann to the animal kingdom. The earlier observers defined a cell 

 as a more or less spherical body limited by a membrane, and containing a 

 smaller body termed a nucleus, which in its turn incloses one or more still 



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