398 THE MICROSCOPE. 



starting-point, find them gradually coalescing, until they meet in a 

 common granule " that of the simple and individual cell." 



Mulder, in describing this starting-point of life, says : " The cell is 

 a concave globule. This concave globule is an individual ; in the most 

 simple form in which it can possibly exist (in the lowest moulds), it 

 possesses all the powers of the molecules united into one whole, and 

 thus reduced to a state of equilibrium. This state depends, not only 

 on the nature of the substances and of their elements, carbon, hydrogen, 

 oxygen, and nitrogen, but also on their form. The state of equili- 

 brium, therefore, could not exist, unless this concave globular form 

 existed. Moreover, this hollow globule possesses the whole of these 

 forces in a state of mutual combination, co-operating for one end ; 

 this being a peculiarity which also apparently depends on the globular 

 form." 



Cells from which plants are formed are very small delicate closed 

 sacs, partaking of many forms, and enclosed in a perfectly transpa- 

 rent membrane, so excessively thin, that it is with difficulty detected, 

 unless iodine or some colouring-matter be previously added. Dead 

 and old cells form an exception, as they become thickened, and the 

 broken surfaces are then readily detected. At one time the cells 

 were said to be developed by an extrication of gaseous matter among 

 mucus ; but the double walls which separate cells are irreconcilable 

 with such an origin. Mr. Thwaites regards the original wall of the 

 cell as a mere shell, having quite a subordinate office to perform in 

 the growth of plants ; and he ascribes all the vital powers of growth 

 to the cytoblast and colouring-matter of the central nucleolus. He 

 supposes the cell-membrane to arise from the action of electrical cur- 

 rents upon mucus, and that fissiparous division is caused by the 

 presence of two centres of electrical force, each giving rise to a set of 

 currents, and producing two cell-membranes instead of the original 

 one. For further information on this very interesting subject, see 

 Henfrey's translation of Mohl's Vegetable Cell; and Dr. J. B. Sanderson, 

 on "Vegetable Reproduction," Cyclopaedia of Anatomy and Physiology. 



The first and most curious exemplification of the simple cell is the 

 fungi known as the Yeast Plant : it consists of two parts, the cell-wall, 

 composed of a matter termed cellulose, and the contents of the cells, 

 resembling fat or oil. The notion that yeast was an organised being, 

 in fact a living plant, was at first strongly opposed by even Berzelius 

 and Liebig ; but by the microscope they have been convinced both of 

 its organisation and vitality. The scientific name by which it is known 

 is Fermentum cervisia, or Torula cervisia ; it consists of globular or 



