October 7, 1910] 



SCIENCE 



457 



have, on the other hand, very sensitive re- 

 actions for potassium, iron, calcium, haloid 

 chlorine and phosphoric acid, and with 

 methods based on these reactions it is pos- 

 sible to localize the majority of the inor- 

 ganic elements which occur in the living 

 cell. 



By the use of these methods we can in- 

 directly determine the occurrence of differ- 

 ences in surface tension in a cell. This de- 

 termination is based on the deduction from 

 the Gibbs-Thoroson 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 surface tension there 

 is less than on the remaining surfaces or 

 walls of the cell. The thickness of this 

 layer must vary with the osmotic concen- 

 tration in the cell, with the specific com- 

 position of the colloid material of the cyto- 

 plasm and with the activity of the cell, but 

 it should not exceed a few hiindredths of a 

 millimeter (0.02-0.04 mm.), while it might 

 be very much less in an animal cell whose 

 greatest diameter does not exceed 20 /a. 



Numerous examples of such localization 

 may be observed in the confervoid proto- 

 phyta. In TJlothrix, 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 

 cases, high on the lateral walls and low on 

 those surfaces adjoining the transverse 

 septa. 



The use of this deduction may be ex- 

 tended. There are in cells various inclu- 

 sions whose composition gives them a dif- 

 ferent surface tension from that prevailing 

 in the external limiting area of the cell. 

 Further, the limiting portion of the cji:o- 

 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 sur- 

 face of the cell, the surface tension is low. 

 It may be urged that the condensation is 

 due to adsorption only, but this objection 

 can not hold, for in the Gibbs-Thomson 

 phenomena the localization 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 adsorption, and is in- 

 deed so regarded.- 



It is in this way that we can explain the 

 remarkable localization of potassium in the 

 cytoplasm at the margins of the chromato- 

 phor in Spirogyra and also the extraordi- 

 nary quantities of potassium held in or on 

 the inclusions in the mesophyllic cells of 

 leaves. In infusoria {Vorticella, Para- 

 mcecium) the potassium present apart 

 from that in the stalk or ectosarc is con- 

 fined to one or more small granules or 

 masses in the cytoplasm. 



How important a factor this is in clear- 

 ing 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 

 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 

 the leaves they accumulate in the meso- 

 phyllic cells in very large quantities, 

 which, if they were not localized as de- 

 scribed in the cell, would affect the whole 

 cytoplasm and alter its action. 



Enough has been advanced here to indi- 

 cate that surface tension is not a minor 

 feature in cell life. I would go even 



-See Freundlich, " Kapillarchemie," p. 50, 1009. 



