Late somati^g£fects are those which manifest them­selves in the5^dividual exposed years after the ori­ginal exposure. The latent period is much longer than for the acute radiation syndrome and is found to be inversely proportional to the absorbed dose. This de­layed response may result from either acute or chronic exposure.

Among the most important late effects are cancers, life span shortening, genetic mutation, embryological

effects and cataracts.

The late stochastic effect of cancer induction is now considered to be the controlling effect in the deter­mination of radiation exposure limits, consequently its study has greater significance to radiological pro­tection than the more dramatic effects of the acute radiation syndrome.

There is no unique disease associated with the long term effects of radiation. The effects express them­selves in human populations as a statistical increase in the incidence of certain already-existing conditions. Because of the low normal incidence of these con­ditions it is usually necessary to observe large popu­lations of irradiated people in order to measure the increase, using statistical and epidemiological tech­niques. In addition to the large number of people needed for the sample, the long latent period provides an added complication which necessitates long term studies.