Reprinted from THE JOUENAL OF BIOLOGICAL CHEMISTRY, Vol. XXIX, No. 3, 1917 



DIRECT DETERMINATIONS OF PERMEABILITY. 



BY R. P. WODEHOUSE. 



(Contributions from the Bermuda Biological Station for Research, No. 60, 

 and from the Laboratory of Plant Physiology, Harvard University, 



Cambridge.} 



(Received for publication, February 23, 1917.) 



It is desirable to determine directly the penetration of sub- 

 stances into the living cell, but in most cases this is difficult or 

 impossible. In order to make such direct determinations it is 

 necessary to compare the composition of the cell sap with the 

 composition of the liquid in which the cell is immersed. In the 

 case of tissues this is impossible, because in crushing the cells 

 to obtain the cell sap the latter is contaminated by admixtures of 

 material from the intercellular spaces as well as altered by chemi- 

 cal action and adsorption. It is therefore necessary to employ 

 individual cells and to extract their cell sap without opportunity 

 for contamination or change. 



Most cells are too small to yield satisfactory results by this 

 method. The writer, however, has been fortunate in having an 

 opportunity to experiment with the marine alga Valonia, which 

 has individual cells so large that it is easy to get from a single 

 cell enough sap upon which to make chemical tests. Cells of 

 the average size yield from 1 to 2 cc. of sap, and it is not unusual 

 to obtain cells which yield as much as 5 cc. 



The cells were removed from the sea water, rinsed in distilled 

 water, dried with filter paper, and then punctured with a needle. 

 On pressing the cell wall the sap squirted out and was collected. 

 This sap is contained in the large central vacuole of the cell 

 (or coenocyte). 



Upon examination the cell sap was found to differ, in most 

 cases, materially from sea water. The sap was taken from a 

 few plants and tested qualitatively for the presence of some of the 

 salts of sea water. 



453 



THE JOURNAL OF BIOLOGICAL CHEMISTRY, VOL. XXIX, NO. 3 



