The bodies of seven stillborn babies were counted for at least 10 hours each. More kinds of radionuclides were found than in the living babies, although the large counting time may have affected the results. The same counting techniques were used with placental tissues from mothers of three of the stillborns. The placenta is the organ that nourishes an unborn child and through which substances from the mother’s bloodstream are exchanged with those in the baby’s blood. The graphs in Figure 17 show data from this experiment and illustrate the method of interpreting whole body counter data. When the counts per minute at each band of gamma-ray energy recorded from the placental tissues (b) were subtracted from corresponding values from the stillborns (a), it was found (c) that the placentas contained more of the isotopes ruthenium-103, ruthenium-106, and zirconium-95 than did the babies that had been nurtured by these placentas. The babies’ bodies contained more niobium-95 and potassium-40 than the placentas. Niobium-95 is produced by the radioactive disintegration of zirconium-95. This suggested that zirconium-95 atoms do not pass readily through the placenta, but, after they have decayed to niobium-95, they pass into the baby’s bloodstream easily. Actually, the gamma-ray energies of zirconium-95 and niobium-95 are so similar that the counter cannot distinguish between them. The two isotopes, however, were separated chemically, and whole body spectra were prepared from samples of the pure elements. The spectrum (d) of pure zirconium-95 subtracted from that of pure niobium-95 was strikingly similar to the spectrum of “stillborn baby minus placenta” on the graphs. Cesium-137 was added to the synthetic spectrum to provide a reference mark at the 0.660-Mev point. This revealed that the ratio of cesium-137 to potassium-40 is lower in babies than in adults. [Illustration: Figure 17 _Results of experiment studying transfer of nutrients from an expectant mother to her unborn child._] Research on Body Processes Radioactive tracer atoms, either natural or purposefully built into molecules of vital materials like proteins, are revealing how these substances function in the body to produce energy or to form new tissues. When we know accurately the normal totals and kinds of radioactive substances in the body, we can undertake new kinds of tracer studies without using large amounts of additional radiation. Small instruments called scanners (see Figure 18) usually are used to track tracer isotopes, but whole body counters are useful in special circumstances. [Illustration: Figure 18 _A multidetector positron scanner to record radiations with opposed pairs of detection crystals. Scanning devices are commonly used for noting the fate of tracer isotopes in medical diagnosis._]