THE PERMEABILITY OF FROG SKIN TO UREA. 

 I. THE INFLUENCE OF NACL AND CACL 2 . 



M. L. BASKERYILL.' 



Although there is already an extensive literature relating to 

 cell permeability, many more facts are needed before an adequate 

 explanation of the mechanism involved can be expected. So 

 much of the work reported has been of a qualitative or even of 

 an indirect nature that additional data are needed on the quanti- 

 tative side, and especially with substances occurring under 

 normal physiological conditions. Accordingly a quantitative 

 study of the penetration of urea through living frog skin under 

 the influence of various reagents has been undertaken. In this 

 paper are reported the effects on the process of different pro- 

 portions of NaCl and CaCl 2 . Experiments with other reagents 

 will be reported in subsequent papers. 



For a number of reasons urea is an excellent substance for 

 use in studying permeability. It is an organic compound 

 occurring normally in animal tissues and fluids and as such 

 belongs to a class needing much more study. It penetrates 

 tissues with moderate ease, entering neither too quickly nor too 

 slowly for experimental purposes. A sufficient amount of urea 

 for quantitative determination passes through the tissues within 

 a period of time that insures the skin's remaining alive and in 

 healthy condition. This point is of much importance because 

 there is reason to believe that some of the papers on the perme- 

 ability of frog skin have reported experiments extending over 

 such a length of time that the skins were killed during their 

 progress. On the other hand, the penetration of urea is not so 

 rapid that the amount may not be decreased by agents having 

 an inhibiting effect on permeability. Of practical importance is 

 the fact that direct quantitative determinations may be made 

 so readily on urea. 



1 From the Laboratory of Physiology of the University of Pennsylvania; the 

 Marine Biological Laboratory, Woods Hole; and the School of Medicine. Uni- 

 versity of Texas, Galveston. 



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