STRUCTURE AND DIVISION OF ORGANIC CELL. 81 1 



active substance of vegetable cells. This term was extended by Max 

 Schultze to embrace all organic cells, and he defined the cell as a nu- 

 cleated mass of protoplasm. At a still later period it was declared 

 that a nucleus was not always present, and the cell was defined as " a 

 structureless mass of protoplasm." 



Such was the stage of the cell-doctrine reached in 1872, thirteen 

 years ago. First the cell-wall had been considered the active element, 

 then the nucleus, and finally the protoplasmic contents, while wall and 

 nucleus came to be considered inessential elements. As Drysdale ex- 

 pressed it about that date, " a cell is like a gun-barrel, without a stock 

 and a lock," Meanwhile Beale had persistently declared that there is 

 no such thing as a cell, in the ordinary sense of the term ; but that all 

 organic bodies are made up of minute particles of living or germinal 

 matter, which consume nutriment and increase internally, while their 

 exterior portions lose vital activity, and become dead or formed ma- 

 terial. These living particles not only grow, but divide, and thus 

 set up new centers of growth, from which emanates new-formed 

 material. 



The division of the cell-protoplasm is, indeed, a most essential part 

 of the life-process, and to it growth and differentiation of tissue are 

 principally due. The cell, when furnished with nutriment, manifests 

 individual growth for a short period. Then it separates into two or 

 more new cells, each of which sets up an individual life. This separa- 

 tion takes place in several methods, of which the most common is by 

 an equatorial constriction, which gradually deepens until it cuts the 

 cell into two sections. Other methods are by the budding off of minute 

 portions from the surface, or the transformation of the cell-contents 

 into many minute germs, which are subsequently set free. 



Such was the cell of thirteen years ago — " a structureless mass of 

 protoplasm," which increased in size by nutrition, and in numbers by 

 division. Such is the cell of most of the text-books of to-day. But the 

 cell of science is a very different affair. Instead of being structureless, 

 it is found to possess an intricate structure, while its division is far 

 from being the simple process above indicated. The new cell-theory is, 

 in fact, but five or six years old in its developed form, and it is as yet 

 settled only in its main features. Its minor details need much further 

 elucidation. 



These new discoveries, which we shall briefly describe, are largely 

 due to the increased power and clearness of definition of the microscope, 

 and still more to new and improved methods of preparing organic sec- 

 tions for investigation, by the employment of stains, preserving agents, 

 and other useful appliances. It is not every microscopist that is able 

 to see the minute details of cell-structure lately announced. The care- 

 ful preparation of material and exceedingly delicate manipulation re- 

 quired need years of practice, and the discoveries referred to are due 

 to the first microscopists of the age, though the methods are now so 



