CHAPTER III. 

 PHYSIOLOGY OF THE CELL. 



A histologic analysis of the organs and tissues of the animal body shows 

 that they can be resolved into ultimate elements, termed cells, which may, 

 therefore, be regarded as the primary units of structure. Though cells 

 vary considerably in shape, size, and chemic composition in the different 

 tissues of the adult body, they are, nevertheless, descendants from typical 

 cells, known as embryonic or undifferentiated cells, the first offspring of the 

 fertilized ovum. Ascending the line of embryonic development, it will be 

 found that every organized body originates in a single cell the ovum. As 

 the cell is the elementary unit of all tissues, the function of each tissue must 

 be referred to the function of the cell. Hence the cell may be defined as the 

 primary anatomic and physiologic unit of the organic world, to which every 

 exhibition of life, whether normal or abnormal, is to be referred. 



Structure of Cells. Though cells vary in shape and size and internal 

 structure in different portions of the body, a typical cell may be said to con- 

 sist mainly of a gelatinous substance forming the body of the cell, termed 

 cytoplasm or bioplasm, in which is embedded a smaller spheric body, the 

 nucleus. Within the nucleus there is frequently seen a still smaller body, 

 the nucleolus. The shape of the adult cell varies according to the tissue in 

 which it is found; when young and free to move in a fluid medium, the cell 

 assumes a spheric form, but when subjected to pressure, may become 

 cylindric, fusiform, polygonal, or stellate. Cells vary in size within wide 

 limit, ranging from 7.7/1 (^-gVo" f an inch, the diameter of a red blood- 

 corpuscle), to 135/4 GrJ-o- of an inch, the diameter of the large cells in the 

 gray matter of the spinal cord). (See Fig. i.) 



The cytoplasm consists of a soft, semifluid, gelatinous material, varying 

 somewhat in appearance in different tissues. Though frequently homogene- 

 ous, it often exhibits a finely granular appearance under medium powers 

 of the microscope. Young cells consist almost entirely of clear cytoplasm. 

 Mature cells contain, according to the tissue in which they are found, 

 material of an entirely different character e.g., small globules of fat, 

 granules of glycogen, mucigen, pigments, digestive ferments, etc. Under 

 high powers of the microscope the cytoplasm is found to be pervaded by 

 a network of fibers, termed spongioplasm, in the meshes of which is con- 

 tained a clearer and more fluent substance, the hyaloplasm. The relative 

 amount of these two constituents varies in different cells, the proportion of 

 hyaloplasm being usually greater in young cells. The arrangement of the 

 fibers forming the spongioplasm also varies, the fibers having sometimes a 

 radial direction, in others a concentric disposition, but most frequently being 

 distributed evenly in all directions. In many cells the outer portion of 

 the cell protoplasm undergoes chemic changes and is transformed into a 

 thin, transparent, homogeneous membrane the cell membrane which 



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