244 



M. L. BASKERVILL. 



tea? 



J & /jortirt/c Cacla 



CHART I. The chart represents the composite results obtained in ten experi- 

 ments. 



The solid line represents the amount of urea in milligrams penetrating the 

 skins in the CaCh-NaCl mixtures. 



The broken line represents the amount of urea in milligrams penetrating the 

 skins in the control experiments when NaCl solution alone was used. 



The dotted line represents the percentage of permeability on the basis of the 

 permeability with pure 0.7 per cent. NaCl solution alone, which is taken to be 

 100 per cent. 



The minimum penetration of urea is obtained with very 

 different percentages of CaCl2 in the various series of experiments. 

 This might be expected from the variability of the tissue to 

 which reference has already been made. With a material like 

 frog skin, composed of many layers of cells, there can be obtained 

 only a rough approximation of the actual proportions of salts in 

 contact with the majority of cells. When one is using skin 

 comparatively permeable to the salts in question, and has 

 washed it in the salt solution for some time before subjecting it 

 to the penetration of urea, the proportions of salts in contact with 

 the cells in the interior of the tissue approach more closely to 

 those of the original solution than is the case at other times. 

 W T ith tissues relatively impermeable to the salts, it takes a 



