The study of endotoxins has undergone cycles of enthusiastic research followed by neglect and revival again due to newly described biological effects attributed to endotoxins. It is almost a generally applicable rule that both extremes in such fluctuations in the popularity of certain re search fields are unjustified. It is obvious that exaggerated expectations will lead to disappointments, and complete neglect of a once-exciting field is to be followed by renewed attention, if the scientific basis of earlier interest was solid and remained so throughout. The healing ef fect of fever was praised as nature's blessed cure, until it was discov ered that it is caused by bacteria. When it became evident that by careful application one can arrive at therapeutic doses without intro ducing shock and hypotension, the era of fever therapy began. During this time, indiscriminate use of pyrogens was so widespread that the high expectations had to be followed by disillusionment. Since then, in terest in endotoxins experienced a few more oscillations, with varying wavelengths and amplitudes, the latest being triggered by the mitotic effect of endotoxin. This led to justified excitement among researchers who study the activation of the cells of the lymphatic system and the consequences thereof, including the release of important mediator mol ecules. Fever therapy is passe, but the healing that often followed the ap plication of endotoxins remains a well-documented fact.

Scientists may feel that there are too many meetings these days, and we tend to agree on this until it comes to our own field of interest. In our own areas we would like to hear about other people's achievements and learn whatever may be helpful in the search for answers to our own pet questions. Exchange of ideas, discussions, and critical evaluations are almost as essential to progress as the actual laboratory work. These were the major motives which initiated our own efforts, with the support of Dr. Earle H. Spaulding, the Chairman of the Department of Microbiology and Immunology at Temple University School of Medicine, to bring to gether for the first time specialists from various disciplines who are attempt ing to achieve the same thing, i. e., the clarification of the chemical and immunological nature of different cellular antigens. Instead of publishing the proceedings of the conference, it was decided that we would attempt to review achievements in the different subjects as well as report the latest developments from our own laboratories. Thus we hope to give scientists involved in this explosively growing field not only an up-to-date report, but also a useful source of relevant references. Despite these efforts and aspirations, we realize that this book is not a complete survey of all known cellular antigens. We tried to present major representations of the most important cell types."