2 INTRODUCTION PEOTOPLASM CELL 



Historical Development of Histology. Modern human histology 

 had its origin in the work of BjdiajLJJ.771-1801). He did not employ 

 the microscope; but his careful and extensive studies of the minute 

 anatomy of tissues gave the impulse and general outline for later studies 

 "by means of the microscope through which mammalian histology has 

 grown to a relatively complete science. Great impetus was given also by 

 the announcement of the 'cell theory' by Schleiden and Schwann in 1839, 

 namely, the statement that all tissues areTcomposed of structural units, 

 or cells. Other epochal steps in histologic science were the recognition of 

 the nucleus by Eobert Brown in 1831, and of protoplasm by v. Mohl 

 in 1846. Cytology arose almost as an incident to embryology. It traces 

 its origin to the work of 0. Hertwig on the fertilization of the sea 

 urchin's, egg (1875). It is the infant anatomic science, its late develop- 

 ment being due, largely, to its dependence upon the optical and me- 

 chanical refinements of the microscope. It deals with fundamental 

 structures within the limits of visibility, and is destined to grow to vast 

 proportions, as the already voluminous literature on 'mitochondria' 

 ('plastosomes') in part foreshadows. 



Relation of Jpstology to Other Biologic Sciences. Histology 

 aims to complete anatomic knowledge. It is thus the complement of 

 gross anatomy. It furnishes also essential preliminary data for the 

 understanding of pathology; abnormal structure and function become 

 fully intelligible only in the light of normal histology. It is funda- 

 mental also to physiology, the science of normal function. 



A certain function demands a specific structure; structure and func- 

 tion sustain reciprocal relationships. Normal function depends upon 

 the normal structure of the cells involved in the function; abnormal 

 function, or disease, is associated with altered cellular structure. His- 

 tology gains enormously in interest and value to the student who will 

 always keep well in mind the function that a certain structure under 

 consideration is called upon to perform. Embryology also to a consid- 

 erable extent builds upon histologic and cytologic data. 



PROTOPLASM 



Chemical Constitution. The unit of both structure and function 

 is the cell. The essential constituent of cells is protoplasm. Protoplasm 

 may be thought of as a physicochemical mechanism. Chemically, it is a 

 very complex aqueous mixture of substances, containing the elements, 



