care being taken to prevent contamination 

 from the cutting. Measurements then were 

 made of the surface radioactivity of the 

 skin, of the muscle layer directly beneath, 

 and of muscle tissues below this at thick- 

 nesses from 5 to 8 mm. The deep muscle 

 was close to the backbone. 



For the radiological measurements, 

 the skin or muscle tissue was enclosed in a 

 cellaphane envelope and placed under an alum- 

 inum plate having a hole 12 mm . in diameter 

 so that the area to be counted on each sample 

 would be constant. The plate was held a 

 fixed distance below a glass Geiger-MUller 

 tube with walls 30 mg./cm 2 . thick for count- 

 ing. 



PASSAGE OF ISOTOPES THROUGH THE 

 SKIN 



Strontium -89 



To observe the passage of strontium -89 

 through the skin of tuna, a series of six tubes 

 was prepared with the skin fastened over one 

 end. The sea water inside the tubes con- 

 tained added strontium -89 to give concentra- 

 tions of 0.01, 0.05, or 0.25 ,uc per ml. The 

 increases in radioactivity of the sea water in 

 the beakers in which the tubes and skins were 

 immersed were measured after 1, 2, 4, 6, 

 and 8 days, during which time the containers 

 were refrigerated. With passage of the iso- 

 tope through the skin, the specific activity 

 of the sea water on the inside surface of the 

 skin should equal that on the outside. Know- 

 ing the expected radioactivity from dilution, 

 the percentages of equilibrium reached with 

 time were calculated. The averages of the 

 different tubes are listed in table 1 . 



Sea water contains appreciable amounts 

 of strontium, and the addition of the radio- 

 active isotope did not significantly increase 

 the total strontium of the water outside the 

 skin . It can be assumed that strontium 



moved across the membraae with an ap- 

 proach to isotopic equilibrium The fact 

 that the experiments were tried with dif- 

 ferent specific activities has no particular 

 meaning in this instance . The approach to 

 equilibrium on the inside of the fish skin was 

 slow. It was only 7 percent complete in one 

 day, and 48 percent complete in 6 days . 



Cesiu m- 137 



Observations were made of the passage 

 of cesium -137 through the fish skin in a 

 similar manner to those employing strontium - 

 89. However, in these the isotope was added 

 to give strengths of . 1 and 1 uc per ml . for 

 convenience in radioactivity measurement. 

 A series of 4 tubes were used at these 

 strengths . The percentage equilibrium 

 reached after 2, 4, 6, and 8 days is shown 

 in table 1 . 



In 2 days the sea water on the inside sur- 

 face of the skin was 51 percent of equilibrium 

 with that outside. This increase in radio- 

 activity continued and reached 92 percent in 

 8 days . It seems that the fish skin offered 

 only a slight barrier to the passage of cesium 

 and that entrance was rapid as compared to 

 that of strontium . 



It should be pointed out that sea water 

 contains only very little cesium (about 2 

 gamma per liter) and that the addition of the 

 cesium -137 increased the total cesium outside 

 the skin considerably, about 150 times in the 

 higher concentration used. There was there- 

 fore a marked gradient for the forcing of 

 cesium across the membrane. This did not 

 exist for total strontium in the tests previously 

 described. In the case of strontium, only the 

 isotopic ratio v/as altered. 



Ruthenium -106 



Sea water, to which had been added 

 ruthenium -106 to give concentrations of .05 ,uc 



