THE STRUCTURAL BASIS OP THE BODY 



twofold structure is also found. So we mav Hofin 



protoplasm containing a nucleus. " * CeU M a 8maU 



Do^bt has often been expressed whptko 

 to our conception of a cell. In Tany of the 

 as the Flagellata among the former and 

 latter, no distinct nucleus can be m^ 

 .sions of the .hole organism are too minute 



of 



* * " " 



and plante - '* 

 """ 



FIG. 2. Ammba protean, an animal consisting of a single naked cell, x 280 (From SEDC 



WICK and WILSON'S Biology.) 

 n, the nucleus ; wv, water- vac uoles ; cv, contractile vacuole ; fv, food-vacuoh . 



made as to the presence or absence of nuclear material. In the larger of them, how- 

 ever, the cytoplasm of the cell contains numerous scattered granules which stain with 

 dyes in the same way as do the nuclei of the cells of higher animals, and these granule 

 possess the resistance to the action of certain digestive fluids which is typical of nuclei. 

 They may therefore be taken as representing the nucleus in the higher forms, 

 in the latter, at certain stages, namely, during the division of the cell, the nucleus 

 breaks up into discrete parts, and there is no reason for believing that such a scattered 

 condition of the nuclear material may not last throughout the whole life of the cell. 



We have defined a cell as a small mass of protoplasm containing a nucleus. 

 Since we shall have to use the term ' protoplasm ' on many occasions in the 

 course of this work, we must have a definite conception of what we mean 

 by it. The term is often used by histologists as implying a substance of 

 certain definite chemical and staining characters. When employed by 

 physiologists it generally implies any material which we can, on a study of its 

 behaviour to changes in its environment, regard as endowed with lift-. 

 Huxley has defined it as " the physical basis of life." Though it may be con- 

 venient to have a word such as protoplasm signifying simply 'living material,' 

 it is important to remember that there is no such thing as a single substance 

 protoplasm. The reactions of every cell as well as its organisation are the 

 resultant of the molecular structure of the matter of which it is built up. 

 The gross methods of the chemist show him that the composition of the 



