DEPARTMENT OF BOTANICAL RESEARCH. 57 



Their changes in form, increase or decrease, division, etc., are inevi- 

 tably affected by the factors described. No conception of matter 

 free from fundamental physical laws can be entertained or success- 

 fully maintained. 



Biocolloids as Membranes; a New Colloidal Cell, by D. T. MacDougal. 



My earlier investigations upon the fundamental mechanism of 

 enlargement of cells and the growth of organs were concerned chiefly 

 with the increases which the solid mass of the protoplasm undergoes 

 by swelling as influenced by the nutrient salts, acids, hydroxides, 

 amino-compounds, and vitamins. The information gained, which 

 has been published in numerous papers, may be taken to apply chiefly 

 to cells in the earliest stage of their development. 



The cell or protoplast of the plant is at first a microscopic mass of 

 a gel in which are included denser bodies or organs, such as the nucleus 

 and plastids. As the protoplast enlarges by swelling or hydration and 

 by the addition of more material, cavities or spaces are formed within 

 it by the process known to the physicist as syneresis, and these cavities 

 persist as vacuoles. The water which fills these clear spaces con- 

 tains solutions of acids, salts, sugars, and amino-compounds of the 

 cell in varying concentrations. While these internal cavities are 

 developing, a dense and tough outer wall of ''cellulose" has been 

 formed around the protoplasm, and these two changes convert the 

 cell into an osmotic machine which pulls liquids into the interior of 

 the cell or loses solutions out through its walls in accordance with 

 the osmotic activity of the various substances concerned and the per- 

 meability of the membranes. The way in which this passage of 

 solutions occurs is largely determined by the character of the firm 

 outer wall of the cell, by the plasmatic layer which lies against it, and 

 by the special membrane or layer which is formed at the surfaces of 

 the wall and protoplasm in contact. These may show widely varying 

 qualities as to permeability. 



In the earlier experiments it was found that a mixture of agar, 

 gelatine, and soaps and lipins in hydration and swelling afforded many 

 profitable parallels with the beliavior of living and dead cell-masses, 

 and as living matter may be safely taken to be made up chiefly of 

 carbohydrates, albuminous substances, and soaps or combinations of 

 the fatty acids with calcium, potassium, or sodium, the experiments 

 were extended to include a study of the influence of a mixture of these 

 colloids on osmosis under conditions similar to those prevailing in the 

 plant cell. 



In carrying out this purpose a new form of artificial cell or osmotic 

 apparatus was devised, which has yielded some results of value in the 

 consideration of the action of the living cell. The living cell has a 

 firm outer wall, which is permeable to the solutions of the salts of the 



