ERNST G. HUF 



209 



All this is informative and significant, but it does not explain 'one-way 

 osmosis'. Although conclusive evidence is lacking as yet, it has been suggested 

 {27,) that 'one-way osmosis' may be understood on the basis of active salt 

 transport. The main reason for this is the dependence of 'one-way osmosis' on 

 the metabolism in skin (22). At least, respiration has to be intact, as must be 

 concluded from results shown in figure 3. One piece of normal, freshly isolated 

 skin was mounted in a differential osmometer and used in a series of osmosis 

 e.xperiments, each of one-hour duration. The experiments were conducted such 

 that inward and outward osmosis alternated. In the intervals between experi- 

 ments, the solutions at the two sides of the skin (Ringer's and 0.2 Ringer's) 

 were renewed. This procedure was carried on for about 15 hours. A final experi- 



100 



50- 



-50- 





20 hrs. 



20 hrs. 



Fig. 3. Influence of aging and of cyanide (0.002 m/I.) on one-way osmosis through isolated 

 frog skin (Rana esciilenta). Buffered Ringer's solution of physiological and | physiological 

 concentration. Average data of 6 experiments each in a and b using two pieces of skin. Further 

 details see text. Vi^o and Vo-.i indicate relative rate of outward and inward osmosis re- 

 spectively (22). 



ment was carried out about 25 hours after the first. When the rate of osmosis 

 in the two directions, in terms of percentage volume change, was then plotted 

 on the ordinate against time on the abscissa, graphs were obtained which are 

 shown in the left half of figure 3. A gain of fluid in one compartment of the 

 osmometer is plotted as a positive volume change; the nearly equal loss in the 

 other compartment is plotted as a negative volume change. The first two sets 

 of data for gain and loss of fluid were set equal to 100. All following readings 

 were expressed as percentages of these original values. It can be seen that, up 

 to about the 15th hour, outward osmosis (solid line) is faster than inward os- 

 mosis (dotted line). From then on, the situation is reversed. When a similar 

 experiment was carried out, except with both saline solutions poisoned by 

 cyanide, it was noticed (fig. 3, right half) that the reversal in the rate of out- 

 ward and inward osmosis had already occurred after about 3 hours. 



