290 CARNEGIE INSTITUTION OF WASHINGTON. 



Osterhout, W. J. V., Harvard University, Cambridge, Massachusetts. Con- 

 tinuation of investigations on permeability in cells. 



A problem important for the understanding of life processes is the nature 

 of selective permeability. Protoplasm absorbs some substances very readily; 

 others penetrate slowly or not at all. Since it is evident that the nature of the 

 penetrating substances determines metabolism it is of importance to know 

 which substances can enter. If we could ascertain this we might draw 

 important conclusions regarding the nature of protoplasm, regarded as a 

 physico-chemical system which allows certain substances to pass while ex- 

 cluding others. 



The ideal method of attacking this problem is to place cells in a solution of 

 the substance to be studied and after a suitable period of exposure to remove 

 them and test their contents for the presence of the substance in question. 

 To do this satisfactorily it is necessary to have large cells whose sap can be 

 obtained without contamination. Hitherto such cells have not been em- 

 ployed. Experiments have been made upon small cells by a variety of 

 methods which have not yielded concordant results, and therefore great 

 confusion has arisen which may be avoided by the use of cells of appropriate 

 size. 



The writer has employed cells of a species of Nitella, which sometimes 

 reach a length of 6 inches. After exposure to a suitable solution they are 

 removed, carefully rinsed, and the sap obtained without contamination by 

 cutting off one end of the cell and squeezing out the contents or by inserting 

 a fine glass tube and removing the sap by suction. The sap is then tested 

 for the presence of the substance which is in the external solution. 



These experiments have demonstrated that, contrary to the views of 

 many investigators, certain salts are able to penetrate protoplasm in its 

 normal state. Further experiments are in progress which are designed to 

 place the subject on a quantitative basis. 



It is also important to study the giving out of substances by the cell. In 

 the case of chlorides, for example, this can be easily accomplished by titrating 

 the cell-sap. Chlorides are absorbed by Nitella from the water and stored 

 within the cell, where the concentration may be 50 to 100 times as great as in 

 the external solution. When the cell is injured the chlorides begin to diffuse 

 out. By making frequent measurements a time curve may be obtained which 

 is of interest. The mathematical analysis of the curve indicates that the pro- 

 cess of injury, followed by death, follows a definite law which appears to be 

 the same as that derived from measurements of the electrical conductivity 

 of the cells. 



An account of this has appeared in the Journal of General Physiology 

 (July 1923). 



