THE OSMOTIC CHARACTERS OF THE CELL 19 



the materials met with in cells enter into it. From the fact that water is not 

 the only body found in the cell it follows of necessity that all materials do 

 not behave in the way that cane sugar, potassium nitrate, and the colouring 

 matter of red beet do ; there must be many materials which are capable of 

 passing through the protoplasm. The researches of later years have proved 

 to us the existence of many such bodies, whose capacity for penetrating the 

 protoplasm may be demonstrated in a great variety of ways. 



The plasmolytic method is equally serviceable lor the demonstration both 

 of permeability and of impermeability. De Vries (1888 a) has shown that 

 glycerine produces plasmolysis at first, but that after several hours this plasmo- 

 lysis disappears, the reason for the disappearance being that glycerine begins 

 slowly to enter into the interior of the cell. When the degree of concentration 

 of the glycerine inside and outside the cell is the same, the turgor of the cell is 

 re-established, and the existence of glycerine on both sides of the cell has as 

 little significance in relation to turgor as if it were entirely absent. The osmotic 

 pressure has, however, increased, and if the cell be once more plasmolysed 

 it will be found necessary to use a more concentrated solution than before. 



Similarly, plasmolysis produced by urea, erythrite, glycol, &c., ceases to 

 make itself apparent, sometimes more rapidly, sometimes more slowly (Overton, 

 1895). Only a few minutes are necessary for the cessation of plasmolysis in 

 Spirogyra when treated with glycol, acetamide, and succinamide, while plasmo- 

 lysis, produced by glycerine, continues for a couple of hours, by urea five hours, 

 and by erythrite twenty hours. Overton has, however, discovered that certain 

 substances, e. g. alcohol, pass through the protoplasm more rapidly than 

 glycol, and produce practically no plasmolysis, behaving in this respect like 

 water. Since the molecular weight of alcohol is 46, a i per cent, solution of 

 that substance has the same osmotic value as a 7-5 per cent, solution of cane 

 sugar, so that, if an 8 per cent, solution of cane sugar produces plasmolysis 

 in a cell of Spirogyra, the same effect should be obtained by using a i-i per cent, 

 solution of alcohol. No plasmolysis is, however, observable on using either a i per 

 cent., 2 per cent., or even 3 per cent, of alcohol, for it passes too rapidly through 

 the protoplasm to give time for plasmolysis to take place. That this result 

 is due really to the rapid penetration of the plasma, and not at all to injury 

 induced by the alcohol, is shown by the fact that if the 3 per cent, solution 

 of alcohol be added to the 8 per cent, solution of sugar, plasmolysis takes place 

 at once just as when the sugar is dissolved in pure water. In a similar way 

 Overton has established the fact that protoplasm is easily permeable to a large 

 number of organic substances, such as ether, chloralhydrate, sulphonal, caffein, 

 antipyrine, &c. 



The fact that many substances enter into the cell in this manner is indis- 

 putable, but their entry is not perfectly self -apparent. We cannot actually 

 see the entrance of he substance, we can only conclude that it enters. At least 

 we must assume this from what has been said, although it does not quite corre- 

 spond with the facts. Not a few of the substances referred to betray their 

 entrance by the changes which are set up by them in the cell, such, for example, 

 as the deposition of insoluble bodies in the cell-sap after the entry of caffein, 

 antipyrine, acetamide, ammonium carbonate, &c. Generally speaking, we are 

 quite ignorant of the nature of these precipitates, save that in certain cases, 

 e .g. caffein and antipyrine, it is known that they are associated with the for- 

 mation of insoluble tannin compounds. Tannin itself is soluble, but, since 

 these tannin compounds are insoluble, the tannin is itself precipitated. In the 

 case of ammonium carbonate, probably the alteration of the acid reaction of 

 the cell-sap only plays a part. This can be proved with greater certainty when 

 the cell-sap is naturally coloured (e.g. as in red beet and in red and blue flowers), 

 the colouring matter serving as an indication of the presence of acids or bases, 

 much in the same way as a solution of litmus would. Thus the entry of very 



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