NORMAL HISTOLOGY 



CHAPTEE I 

 INTRODUCTION-PROTOPLASM THE CELL 



Histology is concerned with the finer structure of living tis- 

 sues. It may thus include the study of both animal and vegetable 

 tissue. 



Animal histology, which deals with the structure of animal 

 tissues, is closely allied to the science of microscopical anatomy, 

 which considers the structure of the organs. 



All tissues are composed of a living substance called proto- 

 plasm, which is of very complex structure. It can usually be 

 considered as being made up of certain structural units. These 

 structural units are the animal cells. 



Protoplasm is capable of all the functions of life metabolism, 

 motion, growth, development, and reproduction. Thus all proto- 

 plasm owes its existence, as does the individual organism also, to 

 a primitive cell mass, the germ cell. This germ cell assumes a 

 more or less definite form, which we may consider as the true cell 

 type the typical cell. The description of the ovum, the germ cell 

 of man, will serve to present those structures which characterize 

 the typical animal cell. 



THE TYPICAL CELL. The term cell, as thus applied, com- 

 prises a circumscribed mass of protoplasm. It is enclosed by a 

 membrane of somewhat denser consistence, the cell wall or cell 

 membrane, which is thickened by a narrow outlying, and often 

 radiating, zone of condensed or otherwise altered protoplasmic 

 substance, the exoplasm. 



The inner portion of protoplasm, that which surrounds the 

 nucleus and is contained within the cell wall, in contradistinction 

 to the peripheral exoplasm, is called endoplasm. 



The term cytoplasm, though used by Kolliker as synonymous 

 with protoplasm, is now limited, in accordance with the usage of 

 Strasburger, to the entire protoplasmic substance of the cell, ex- 

 clusive of its nucleus. 



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