THE CELL. 7 



The vegetable cell is known from the animal cell by the presence 

 of cellulose. 



The cell of the vegetable kingdom in its respiration takes in 

 oxygen and gives off carbonic acid, as we do, but in its nutrition the 

 action of the sun's rays upon the chlorophyll causes it to break up 

 the carbon, to fix it in the tissues, and to give off oxygen. This 

 fixation of carbon overshadows in daylight the ordinary respiration of 

 the plant, which goes on both by day and by night. Yeast-cells break 

 up sugar into alcohol and carbonic acid. Besides this action, they 

 have in them a ferment, invertin, which changes cane-sugar into 

 invert-sugar, which is a mixture of dextrose and laevulose. 



CELLS. 



We have learned that the higher forms of life, whether plants or 

 animals, may be resolved into a vast number of very small, structural 

 units, called cells. The skin, muscles, bone, brain, etc., appear to 

 the naked eye to be composed of one kind of substance respectively. 

 The microscope, however, has told us that each tissue is composed of 

 colonies of units, held together by intercellular cement, and that the 

 units or cells of a particular tissue are similar in structure and func- 

 tions. For example, upon examination, we find that muscular tissue 

 is made up of ribbonlike fibers, similar in appearance and structure 

 and all engaged in the same function contraction. Thus, the cell 

 is not only the unit of structure, but also of function, diseased or 

 normal. 



Animal cells are of various sizes. Although differing very much 

 in shape and appearance in various parts of the body, nevertheless 

 every cell consists of the following parts: (1) protoplasm, (2) nu- 

 cleus, (3) centrosomes, and (4) various matters commonly called 

 "special cell-constituents." 



Max Schultze's definition of a cell, enlarged fey later research, is : 

 "A mass of protoplasm containing a nucleus/' 



The term cell as employed to-day is a misnomer, but from its 

 constant use since the seventeenth century, it has gained such a hold 

 upon the minds of those engaged in the study of science that the 

 attempt to supersede it with a more appropriate term has been unsuc- 

 cessful. However, the idea that it originally conveyed has been some- 

 what modified. The term originated among the botanists of the 

 seventeenth and eighteenth centuries, and was applied to chamberlike 

 elements, separated from one another and containing a fluid. Their 

 characteristic and most important feature was the wall, or membrane, 



