2. ELEMENTS OF STRUCTURE, 



A. The Cell. 



45. 



THOSE anatomists of recent times who seek with the assistance of our 

 improved microscopes an insight into the minute structure of the human 

 and animal body, have all arrived at this conclusion, however widely 

 their other scientific views may differ, that " the cell," cellula, is the most 

 important of all the structural or form-elements of the system. This fact, 

 although surmised by earlier observers, who recognised the structure in 

 question under the name of "vesicle," was first firmly established by 

 Schwann. Following up Schleideris discoveries in vegetable anatomy, he 

 showed the cell to be the starting-point, in the broadest meaning of the 

 term, of the animal body (see above, p. 4). This is the greatest discovery 

 ever made by the aid of the microscope. 



Present-day investigation tends more and more to confirm the correct- 

 ness of this proposition of Schwann, that the cell alone, and by itself, 

 must be regarded as the primordial structural element of our frame, and 

 that all the various other elementary parts to be found in the mature body 

 are originally derived from the cell. 



The first point, then, to be attended to here is, to obtain a correct im- 

 pression of what is meant' by a " cell," and what by a " structural 

 element." 



By " form constituents," " form elements," " elementary parts," or 

 " structural elements," we do not by any means understand (as might be 

 incorrectly inferred from the terms) the smallest particles of the body re- 

 cognisable by the microscope in the shape of granules, vesicles, or crystals. 

 A form-element is rather the last, or contemplating the subject from 

 another point of view, the first anatomical unit : a combination of the 

 most minute particles to form the smallest organic apparatus. Struc- 

 tural elements are the first representatives 

 of organic activity; they are, consequently, 

 physiological as well as anatomical units ; 

 they are "LIVING THINGS." 



But what is the cell? This question 

 cannot be answered in a word, but re- 

 quires to be met with a somewhat detailed 

 description. 



The cell (fig. 40) is a microscopically 

 small, primarily spheroidal body, which 

 often assumes, however, other forms, and which consists of a soft mass 



c 



Fig. 40. Two cells of round or oval form. 

 a a, border of the cell ; 6 6, cell body ; 

 c c, nuclei with nucleoli, d d. 



