NEW FRONTIERS IN THE ATOM — LAWRENCE 167 



very well also for the thyroid, as is shown in plate 2, which is a 

 photomicrograph of a thin section of thyroid tissue containing 

 radio-iodine; alongside is the radio-autograph obtained from the 

 same microsection by placing it against a photographic plate. The 

 distribution of the iodine in various parts of the gland is shown in 

 surprising detail. 



Similarly striking radio-autographs of the distribution of phos- 

 phorus and strontium in rats are shown in plate 3, figure 1. Here 

 two rats were fed radiophosphorus and radiostrontium respectively, 

 and then some hours or days later they were sacrificed, and frozen 

 sections of the entire bodies of the animals were placed against a 

 photographic plate. The resulting radio-autographs show clearly 

 that both strontium and phosphorus are selectively deposited in the 

 bones, phosphorus being more widely distributed in other tissue. 

 The distribution of the strontium in the bones also appears to be 

 quite different from that of phosphorus as radio-autographs of the 

 sections of bones clearly show (pi. 3, fig. 2). 



These examples serve to illustrate the power of the new technique 

 of radioactive tracer atoms. It has often been said that the progress 

 of science is the progress of new tools and new techniques, and I 

 think we may look forward to accelerated developments in biology 

 resulting from the tracer elements. 



ARTIFICIAL RADIOACTIVE SUBSTANCES IN THERAPY 



It is somewhat afield for me to discuss medical problems, but I 

 should like to direct your atention to the possibilities of the artificial 

 radioactive substances in the treatment of cancer and allied diseases. 

 It is well known that at the present time there are two main ap- 

 proaches to the treatment of neoplastic disease, surgery and radia- 

 tion. It is sometimes possible to cut out a cancer completely and 

 effect a cure, and in other circumstances, it is possible to destroy a 

 tumor by irradiation with X-rays or radium. The mechanism 

 whereby the radiation destroys the tumor without destroying an 

 excessive amount of surrounding normal tissue is doubtless extremely 

 complicated, but in any case it is evidently important to localize the 

 radiation to the tumor as much as possible. Perhaps the idea would 

 be approached if a means were at hand to irradiate each and every 

 malignant cell without irradiating a single normal cell. 



The artificial radioactive substances open for the first time the 

 possibility of an approach to such selective irradiation of tissue. 

 The above examples of tracers suggest the treatment of thyroid 

 tumors with radioactive iodine, bone tumors with radioactive 

 strontium and radioactive phosphorus. These possibilities are being 

 investigated as is the more specific problem of finding a radioactive 



