CHAPTER II 

 THE CELL 



DURING the latter part of the seventeenth century the simple micro- 

 scopes of the day demonstrated that plants were composed of small 

 box-like spaces surrounded with a distinct wall, and filled with liquid. 

 The name of cell was given to these. In 1839 Schwann put forward 

 the theory that the animal body was built of cells. The identity of 

 protoplasm in all forms of life, plant and animal, was established, and 

 the cell defined as a nucleated mass of protoplasm. The cell may 

 be regarded as a working unit of protoplasm. 



The body of a cell consists of a substance called protoplasm or cyto- 

 plasm (Fig. 6). In the young living egg cell (such as echinoderm ova), 

 the structure appears homogeneous, like egg white; while in older 

 cells it appears alveolar or reticular. To bring structures into view, 

 and to enable thin sections of organs to be cut, fixing and staining 

 reagents are used. The reagents which are used to fix and harden 

 tissues for microscopical examination, such as alcohol, a saturated 

 solution of mercuric chloride, etc., coagulate protoplasm and produce 

 thread-like and granular precipitates in cells artefacts which 

 often produce appearances of structure not existing in the living cells. 

 Such granules and fibres appear in homogeneous solutions of egg white 

 or peptone when treated with hardening reagents. We must not 

 draw conclusions as to cell structure without comparing the fixed with 

 the living cell. The same method of hardening i.e., the same chemical 

 process can, however, be justly used to compare the structure of 

 normal with that of abnormal organs. Reagents can also be used 

 to inv3stigate the chemistry of the cells ; to identify in them by different 

 staining reactions fat, glycogen, iron, potassium, etc. This is a 

 valuable method of microscopical study. The essential structur3 of 

 a living cell appears to be a homogeneous fluid material studded with 

 a large number of minute granules (Fig. 7). Between these two phases, 

 granule and fluid, physico-chemical changes take place which manifest 

 themselves in the life of the cell. The foam structure of protoplasm 

 can be closely imitated by rubbing up oil with potash or sugar into a 

 very finely divided paste. A drop of this is put into a drop of wat^r 

 on a microscopic slide. The water is attracted by the osmotic pressure 

 of the potash or sugar and produces the foam. Radium bromide powder 

 dropped into a gelatin and broth medium produces cell -like structures 

 which increase in size and divide, multiplying, apparently, like a living 

 organism. The radium gives off an emanation, the product of its 



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