Un compagnon de la United States pharmacopia ; . la cellule vide-mur, qui est sans vie que nous verrons tout à l'heure d'apprendre. Cette utilisation conventionnelle de l'termcell est parfaitement acceptable, mais nous devons garder la distinction à l'esprit. Le cell-wall est formée à partir du protoplasme, et n'est pas vivant ou tak-ing en partie les fonctions de la vie sauf dans le sens qu'un cheveux sur thehead ou la fin de l'ongle d'un doigt est vivant. Il s'appelle formedmaterial, et, une fois formé, reste généralement longtemps après que toute vie ou activityhas ont cessé dans l'article. La taille des cellules végétales est extrêmement variable, whil

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A companion to the United States pharmacopia; . the empty cell-wall, which is with-out life as we shall presently learn. This conventional use of the termcell is perfectly permissible, but we must bear the distinction in mind. The cell-wall is formed from the protoplasm, and is not living or tak-ing part in the functions of life except in the sense that a hair on thehead or the protruding end of a finger-nail is alive. It is called formedmaterial, and, once formed, usually remains long after all life or activityhas ceased in the part. The size of vegetable cells is extremely variable, for while the aver-age cell is stated by Carpenter to be about 0.085 millimeter (^^ inch)in diameter, there are others fully 0.85 millimeter (^ inch), and someless than 0.0085 millimeter (^-qVtf inch) in diameter. We will first consider the cell contents. When the cell is young itis completely filled with protoplasm, a portion of which may be differ-entiated from the remainder so as to form the nucleus. The cell-wall UNITED STATES PHARMACOPOEIA. 1069. mav not yet be formed in the cells earlier stages, when a delicate layerof protoplasm on the outer surface envelops the remainder but still re-mains a part of the whole protoplasm. This soon becomes surroundedwith the denser wall of cellulose, but may be separately shown by con-tracting the protoplasm by any medium which will abstract water fromit, as alcohol, syrup, glycerin, orstrong acids. In the illustration thecontracted protoplasm in cells fromthe pulp of rhubarb root is shown.The delicate membrane surroundingit, but which is formed by the actionof the reagents, is sometimes spokenof as the primordial utricle. As the cell grows older and larger, spaces occur in the protoplasm whichare filled with a more watery fluidand which are termed vacuoles. The watery fluid is the cell-sap, which i .., , , Fig. 571.—Parenchyma Cells of Rhubarb, increases in volume until the proto- mounted in balsam, two empty, the othersplasm occupies only a sm

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