4 BACTERIOLOGY. 



met with in the cell ; while it must be admitted 

 that at the present time we can only in a limited 

 sense regard the granules composing the cell 

 as endowed with the peculiar properties of life. 

 If there exist cells composed solely of proto- 

 plasm (Monera, Haeckel), which contain, that 

 is, only the " granules," or the threads, mesh- 

 work, or froth constructed out of these par- 

 ticles, such cells theoretically would be the 

 least differentiated, and might be regarded as 

 those from which the higher forms have been 

 developed. It was supposed for a time that 

 free cells of this kind, consisting wholly of pure 

 protoplasm, existed in the form of Haeckel's 

 " Urschleim" but the existence of such struc- 

 tures has not been confirmed. 



Bodies which are undoubted cells all show 

 some degree of differentiation. Indeed, animal 

 cells always, and plant cells almost always, con- 

 tain a definite rounded body called the nucleus. 

 Only some of the lowest plant cells appear to 

 be devoid of a nucleus. Many cells, especially 

 plant cells, are surrounded by a dense wall or 

 cell-membrane. Many cells also contain vac- 

 uoles,- either true cavities or cavities filled with 

 fluid ; and frequently granules other than pro- 

 toplasm are found associated with the cell-sub- 

 stance, the name paraplasm or deutoplasm 

 being given to these particles. These mor- 



