methods and can be measured only by instruments that are designed to count nuclear radiations. For example, the amount of gr90 that has fallen out of the stratosphere and onto the continental United States has been less than @ pound and a half or approximately one gram per 5,000 square miles (calculated on the basis of 30 millicuries per square mile and 5 x 106 square miles in the continental United States). be found, Sr?° from this pound and a half source can by radiological methods, in milk, wheat, bone samples collected throughout the nation, plant and but the amount in any one sample is too small to be weighed even by the most sensitive balance. In biological work, a curie is often too large an amount of radioactivity to be expressed simply, so the unit of radioactivity is often expressed as a fraction of a curie, e. g., a millicurie (mc), one one-thousandth of a curle; or a microcurie (uc), one one-millionth of a curie; or even a micro-microcurie (wuc), which ig equal to 2.2 disintegrations per minute. The curie is the rate at which energy is being released from nuclei of atoms regardless of whether the energy is being released as alpha or beta particles, gamma