Chromosomes. being well-defined structures that are easily vis ible under the optical microscope. readily lend themselves to in tense physical and biochemical study. The understanding of the structure and function of this most critical genetic material has progressed through a number of interesting stages. Often connected with the development of new techniques in staining and photography. using the standard microscope and the electron microscope. It is interesting to look back at the history of cytogenetics. I would like especially to emphasize the work of Karl Sax and many of his students. Work with Tradescantia became feasible after Edgar Anderson straightened out the ecology and Sax took advantage of the small number of chromosomes easily visible under the microscope. As a matter of fact. this development is seen as the foundation for the quantitative analysis of radiation effects on chromosomes. During the 50 years since then.- more refined studies have been initiated. The study of cytogenetic mechanisms has become an important tool for the recognition of the effects of environmental factors on all liv ing systems and has made SCE studies possible. One of the most important stages in chromosome research was the development, in radiation biology, of radiolabeling the chromosome with tritiated thymidine. This technique. published in 1957 by Dr.

The study of the relationship between environmental pollution and human health is in its infancy. The number of substances and mixtures that have been identified in uncontrolled hazardous waste sites or that have been in advertently released into the environment is large and data on how thes~ substances are modified as they interact with one another as they migrate through soil, air, and water are limited. There are also limits on our un derstanding of how these substances may be ingested, inhaled, or absorbed by people. The complexity of possible interactions between biological, chemical, and physical components in a given environment makes it virtually impossible to evaluate the potential for adverse biological effects ade quately in the laboratory. Other, more comprehensive methods which provide realistic and interpretable results must be used. Many scientists believe that humans represent the ultimate sentinel species of a toxic exposure re sUlting from environmental pollution, however such exposures may also se verely impact environmental health. There exists a wide variety of organ isms in the natural environment that could be used to provide an early warning for potential human health effects as well as to indicate adverse ecological effects. The issue of effective utilization of sentinel species for environment al monitoring is a rapidly developing area of research which has grown in importance during the last decade.

For at least 40 years there has been a great interest in the problems created by infectious airborne agents and other toxic sub stances transported through the air. During the Second World War, this problem grew out of the very high incidence of upper respira tory infections appearing in new military recruits who were brought together in very large, open quarters. As a result, very interest ing methods were developed to measure these airborne agents, espe cially bacteria, and some important methods were refined for their control. These methods primarily concentrated on ultraviolet radia tion, propylene glycol and other means to reduce the dust in an en vironment. Because of the specialized circumstances at that time the whole consideration of airborne particles became prominent. Now, with the new strides in the recognition of mutagenic and carcinogenic effects attributed to exposure to airborne chemicals from today's technology, the problem has again become quite promi nent. The development of experimental chambers has made it possible to conduct studies under carefully controlled conditions."