MODERN CONCEPTIONS OF CELL-STRUCTURE 



AND FUNCTION. 



By HAROLD A. HAIG, M.B., Lond. ; M.R.C.S., Eng. 



(Lecturer in Histology and Embryology, University College, Cardiff.) 



Nowadays, the study of the complex problems 

 dealing with cell-organisation and function is be- 

 coming more and more important and in certain 

 branches of biology, notably pathology and bacterio- 

 logy, is one which becomes intimately connected 

 with abnormal processes in the cell ; these processes 

 are only to be correctly interpreted when the inner 

 workings of the normal cell are understood, and 

 in but few instances can it be said that the 

 normal phenomena 

 are fully explained. 

 In the present article 

 it will be my object 

 to place before the 

 reader a few of 

 the more modern 

 ideas with regard to 

 the structure and 

 function of the cell, 

 and to try and ex- 

 plain the reasons 

 why a normal cell- 

 unit when subjected 

 to morbid influences 

 should have its life- 

 cycle so profoundly 

 altered as to produce, 

 either in the indi- 

 vidual cell or cell- 

 aggregate, signs of 

 obvious functional 

 derangement. 



At the outset, it 

 should be remem- 

 bered that a typical 

 cell, whether animal 

 or vegetable, is made 

 up structurally of at 

 least four parts (see 

 Figure 14) viz. : — 



a. The cytoplasm. 



b. The nucleus, an 



oval or spher- 

 oidal body situated somewhere in the cyto- 

 plasm. 



c. The plastids, small living structures concerned 



with the manufacture of various foods in the 

 cell. 



d. The vacuoles ; these are spaces filled with fluid, 



usually a watery solution of salts, certain pro- 

 teins, organic acids,sugars, and so on (cell-sap). 

 The cytoplasm, nucleus, and plastids constitute 



TTL 



Figure 14. 

 Diagram of a typical cell (stained with nuclear and plasmic stains) 



a. Cell wall: not always present ; ect. Ectoplasmic layer of cytoplasm : this is often present 

 in plant cells; s/>. Spongioplasinic network of cyptoplasm, upon which minute granules or 

 " microsomata" are to be seen ; hy. Hyaloplasm; g. Granules, either of the nature of 

 zymogen-granules or Altmann's (see text) ; 6. Vacuoles ; f>I. Plastids ; M. Metaptasm 

 granules (starch, protein, etc.); k. Kinoplasm ; w. Nucleus showing (/) clear nuclear plasm 

 (rV) Linin network (in) Chromatin-granules and Karyosomes (iv) Plasmosomes or nucleoli, 

 the whole surrounded by the nuclear membrane. c. The centrosome (doubled). 



the protoplasmic portions of the living cell or proto- 

 plast : the cytoplasm is often, especially in vegetable 

 cells, surrounded by a firm cell-membrane composed 

 either of carbohydrate material (cellulose) or of a 

 rather firmer protoplasmic substance derived from 

 the outer part of the cytoplasm (ectoplasm). The 

 animal cell is, however, rarelv enclosed by a complete 

 cell-membrane, and this membrane, when present, is 

 never composed of cellulose. 



In its elementary 

 structural details, as 

 put forward above, 

 there is very little 

 difference between 

 the plant and the 

 animal cell ; but in 

 ultimate function 

 there are often very 

 marked differences, 

 the most well known 

 of these being per- 

 haps those connected 

 with the presence in 

 the plant cell of the 

 chloroplasticls, the 

 small oval protoplas- 

 mic structures which 

 contain the green 

 pigment chlorophyll. 

 The chloroplastids 

 are thus able, by 

 virtue of their pos- 

 session of this pig- 

 ment, to utilise a 

 portion of the radiant 

 energy of white 

 light, and to turn 

 this energy to ac- 

 count in furthering 

 the decomposition of 

 carbon dioxide and 

 water by the plastid, 

 the ultimate result 

 being the formation, by means of chemosynthetic 

 reactions, of some form of sugar (probably dextrose). 

 The animal cell rarely, if ever, possesses chlorophyll; 

 and in those instances where chlorophyll-containing 

 bodies are found in an animal cell (Hydra, Euglena 

 and other Flagellata), these almost always turn out 

 to be members of the Volvocaceae which appear to 

 be living in symbiotic connection with the animal 

 cell. This being so, the animal cell is not able by 



