A SCIENTIFIC CAREER 29 



observed by us as well. These were among the first application of radio- 

 active tracers in radiobiological studies. Our joint investigations, among 

 others, were extended to the determination of the number of fertilizing 

 asp pollen, the atoms of which can be located in a seed. The incorporation 

 of 3'-P into DNA of the nucleated erythrocytes of the hen was found, 

 in collaboration with Ottesen about the same time, to be quantitatively 

 conserved during the lifetime of the erythrocytes, which enabled us to 

 measure the life-cycle of the red corpuscles of the hen. 



Prior to and during the war I saw a lot of August Krogh, famous 

 physiologist and a man of great kindness, to whom I was much indebted. 

 While staying in Stockholm, he wrote down a detailed program of 

 further permeability studies in which radioactive tracers would have 

 to be applied. It is much to be deplored that he could not witness the 

 great further success of his eminent pupil Ussing in this field. 



Radioactive Carbon 



My chief activities since 1943 have been in Stockholm and, for some 

 years after the war, in Copenhagen too. During the last years I have 

 been attending solely to my laboratory in Stockholm. I extended the 

 radiation studies to the measurement of ^'*C incorporation into DNA in 

 the organs of growing mice, which was found to be depressed in contrast 

 to incorporation into proteins. My colleague Forssberg and I studied 

 the effect of irradiation on bicarbonate, glucose, and fatty acid meta- 

 bolism and other problems, applying i^C as a tracer. These studies, among 

 others, led to the discovery of a fatty acid fraction of the liver having a 

 very rapid turnover rate. For the last years we have been interested 

 in physiological and clinical problems of iron metabolism. 



In 1953 I had the privilege to deliver the Aschoff Memorial Lecture, 

 which is given each year in the University of Freiburg to commemorate 

 the great pathologist. Aschoff was not only one of the great pathologists 

 of this century but a man of great wisdom and vision. The British patho- 

 logist Robert Muir wrote in his obituary- note on Aschoff, published 

 during the war, "I think one may say that in the period since Virchow's 

 time, he has been the outstanding figure." Aschoff showed some interest in 

 our early work with lead and w as quite enthusiastic about the determina- 

 tion of the volume of the body water by applying heavy water as an 

 indicator, which was the first clinical application of isotopic tracers. 

 In my Lecture I mentioned that our investigations had led us to the 

 conclusion, not unanimously accepted by the audience, that the forma- 

 tion of haemoglobin is not radiosensitive, that so long as erythropoetic 

 cells with an incomplete haemoglobin cotitent are present in the bone 

 marrow, even if the organism is exposed to Roentgen radiation, additional 

 hemoglobin is laid down in these cells. Since then this conclusion has 



