X-Ray Sensitivity 113 



counts over the sacrum rise fairly steadily over the first 6 hours, indica- 

 ting uptake of iron into the bone marrow; over the spleen there is a 

 slight fall; over the liver the counting rate is fairly constant. But in a 

 patient having an anaemia M'ith a hypoplastic marrow, where there is 

 very little marrow activity, one finds that the counts over the sacrum 

 fall because there is very little uptake of the iron in the marrow. On 

 the other hand, the counts over the liver and over the spleen rise very 

 rapidly, and in the case of the liver, and to a certain extent the spleen, 

 there is a storage of iron. The work is so far unpublished. 



Summing up, I feel that from the point of view of studies of whole 

 body irradiation on animals, ^^Fe is likely to be very useful indeed. 



ISOTOPES 



