746 TRANSACTIONS OF SECTION I. 



but we have as yet no delicate microchemical tests for sugars, urea, and other 

 nitrogenous metabolites, and in consequence the part they play, if any, in altering 

 the surface tension in different kinds of cells, is unknown. Further research 

 may, however, result in discovering methods of revealing their occurrence micro- 

 chemically in the cell. We are in a like difficulty with regard to sodium, whose 

 distribution we can determine microchemically in its chief compounds, the 

 chloride and phosphate, only after the exclusion of potassium, calcium, and 

 magnesium. We have, on the other hand, very sensitive reactions for potassium, 

 iron, calcium, haloid chlorine, and phosphoric acid, and with methods based on 

 these reaction;: it is possible to localise the majority of the inorganic elements 

 which occur in the living cell. 



By the use of these methods we can indirectly determine the occurrence of 

 differences in surface tension in a cell. This determination is based on the 

 deduction from the Gibbs-Thomson principle that, where in a cell an inorganic 

 element or compound is concentrated, the surface tension at the point is lower 

 than it is elsewhere in the cell. If, for example, it is concentrated on one wall of a 

 cell. The thickness of this layer must vary with the osmotic concentration in the 

 cell, with the specific, composition of the colloid material of the cytoplasm and 

 with the activity of the cell, but it should not exceed a few hundredths of a 

 millimetre (0'02 to 0'0-t mm.), while it might be very much less in an animal cell 

 whose greatest diameter does not exceed 20 yu . 



Numerous examples of such localisation may be observed in the confervoid 

 Protophyta. In Ulothrix, ordinarily, there is usually a remarkable condensation 

 of the potassium at the ends of the cell on each transverse wall. The surface 

 tension, on the basis of the deduction from the Gibbs-Thomson principle, should 

 be, in all these crises, high on the lateral walls and low on those surfaces 

 adjoining the transverse septa. 



The use of this deduction may be extended. There are in cells various inclu- 

 sions whose composition gives them a different surface tension from that prevailing 

 in the external limiting area of the cell. Further, the limiting portion of the cyto- 

 plasm in contact with these inclusions must have surface tension also. When, there- 

 fore, we find by microchemical means that a condensation of an inorganic element 

 or compound obtains immediately within or without an inclusion, we may conclude 

 that there, as compared with the external surface of the cell, the surface tension 

 is low. It may be urged that the condensation is due to absorption only, but this 

 objection cannot hold, for hi the Gibbs-Thomson phenomena the localisation of 

 the solute at a part of the surface as the result of high tension elsewhere of the 

 solution is, in all probability, due to absorption, and is indeed so regarded. 1 



It is in this way that we can explain the remarkable localisation of potassium 

 in the cytoplasm at the margins of the chromatophor in Spirogyra and also the 

 extraordinary quantities of potassium held in or on the inclusions in the meso- 

 phyllic cells of leaves. In Infusoria (Vorticella, Paramoecium) the potassium 

 present apart from that in the stalk or ectosarc is confined to one or more small 

 granules or masses in the cytoplasm. 



How important a factor this is in clearing the active portion of the cytoplasm 

 of compounds which might hamper its action, a little consideration will show. 

 In plants very large quantities of salts are carried to the leaves by the sap from 

 the roots, and among these salts those of potassium are the most abundant as 

 a rule. Reaching the leaves these salts do not return, and in consequence during 

 the functional life of th9 leaves they accumulate in the mesophyllic cells in very 

 large quantities, which, if they were not localised as described in the cell, would 

 affect the whole cytoplasm and alter its action. 



Enough has been advanced here to indicate that surface tension is not a minor 

 feature in cell life. I would go even further than this and venture to say that 

 the energy evolved in muscular contraction, that also involved in secretion and 

 excretion, the force concerned in the phenomena of nuclear and cell division, and 

 that force also engaged by the nerve cell in the production of a nerve impulse 

 are but manifestations of surface tension. On this view the living cell is but a 

 machine, an engine, for transforming potential into kinetic and other forms pf 

 energy, through or by changes in its surface energy. 



1 Sec Frcundlich, KapMlarchemie, p. 50, 1909. 



