338 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



by necessary nutrient requirements. Thus one is enabled to experi- 

 ment indefinitely upon various tissues and cells. An outstanding 

 example of a contribution by this technique was that made by Dr. Ross 

 Harrison, of Yale. He was able to show, for example, that all the 

 cells of a developing nervous system were independent of one another 

 and did not unite in a common syncytium. This tissue technique has 

 many ramifications under varying experimental approaches. 



ISOTOPES 



The most recent types of technique in microscopic anatomy are 

 those concerning tracer isotopes and autoradiographic procedures. 

 The fondest hopes and dreams of scientists have been to determine 

 accurately the presence of any particular substance at a given time 

 within certain tissues of plants and animals. Not only have they been 

 used to determine accurately the presence of such substance, but 

 also as a method showing how the plant or animal organism metabo- 

 lizes these materials. By radioactive isotopes, one can, either by the 

 o-eieer-counter method or autoradiographic techniques, determine 

 the presence and amount of any substance that is either naturally auto- 

 radioactive or artificially made so. One of the most common uses 

 of radioactive isotopes in this particular field has been to determine 

 the uptake of iodine by the thyroid gland. By giving radioactive 

 iodine to an individual, the amount of iodine absorbed in the gland 

 can be determined. Under experimental and normal conditions, one 

 can determine to a certain extent the manner by which the thyroid 

 gland utilizes iodine. These new techniques are used not only in 

 tracer work but also in therapy. For example, the administration 

 of radioactive iodine to a patient suffering from cancer of the thyroid 

 gland will alleviate, and, in certain instances, cure the cancer. 

 One of the most striking examples of this technique is the study in 

 which the body metabolizes radium. It has been known for many 

 years that radium, strontium, and barium have a great affinity for 

 bone. Investigators would like to establish positively whether radium 

 behaves as calcium does. 



In our own laboratories, for example, Dr. Frank Hoecker and the 

 senior author of this paper have shown that radium is not distributed 

 evenly or uniformly throughout the bone either in the rat or in man. 

 We have devised techniques where we can, by autoradiographic 

 methods, determine accurately in space, not only the presence of 

 radium but the amount found in bone after its administration into 

 the body. Our technique is one in which we determine photographi- 

 cally by our autoradiographs the presence of radium in any particular 

 spot by superimposing the photomicrogram of the bone and the 



