/ • 



Chapter I 



INTRODUCTION 



Historical sketch:- It is well known that the cellular organiza- 

 tion of living things was first recognized by the English engineer, 

 Robert Hooke (1665), who, toward the end of the seventeenth 

 century, was looking at sections of cork with a view to finding out 

 what applications could be made of the recent discovery of the 

 microscope. He described the tissue as formed of alveoli resem- 

 bling a honey-comb. These alveoli he called cells. For a long 

 time, however, the significance of this structure was not under- 

 stood. The French botanist, Brisseau de Mirbel (1833) thought 

 that cellular tissue was composed of vacuoles hollowed out of a 

 homogeneous substance, which corresponded to living matter. It 

 was MOLDENHAWER (1812) who, for the first time, demonstrated 

 the individuality of cells. Having suxiceeded in separating the 

 elements of tissues by maceration, he proved that cells have a wall 

 of their own and cannot, therefore, arise as cavities in a homo- 

 geneous substance. Later DUTROCHET (1824), TURPIN (1827) and 

 Meyen (1830) considered cells as moi'phological entities but their 

 attention had been centered rather on the walls than on the con- 

 tents of the cells. In 1830 Meyen had discovered chlorophyll 

 grains, starch grains and crystals within the cavity of the cell. 

 In 1831 the English botanist, Robert Brown, who gave his name 

 to Brownian movements, discovered the nucleus in the epidermal 

 cells of orchids. Shortly after (1838), Schleiden, the promul- 

 gator of the cell theory, attributed predominating importance to 

 the nucleus to which he gave the name Cytoblast and which he 

 considered as the generator of the cell. According to Schleiden, 

 a cell is formed as follows: in a matrix, the cytoblastema, there 

 appears the cytoblast on whose surface a membrane then becomes 

 diflferentiated which lifts itself up like a watch crystal, grows, and 

 bursts away from the cytoblast, leaving an empty space into which 

 the matrix penetrates by filtration. 



DuJARDiN (1835), in the cells of Infusoria, first accurately 

 described living matter, to which he gave the name sarcode. 

 Nageli (1866) perceived in addition that plant cells are occupied 

 by nitrogenous matter and voN Mohl at the same time described 

 it under the name of Protoplasma and attributed to it a primary 

 importance. According to this observer, the plant cell, made up 

 of the protoplasm, contains a nitrogenous primordial utricle, lining 

 its wall on the inside and enclosing the nucleus. This primordial 

 utricle is the seat of special movements already seen by B. CORTI 

 (1772) and Treviranus (1807). The rest of the cell is occupied 

 by cell sap. 



