During the past several years there has been a shortage of flight opportunities for biological and medical projects. And those that were available usually had severe restrictions on instrumentation, number of subjects, duration, time allotted for performing the experiments, a possibility for repetition of experiments. It is our hope and expectation that this will change once the international Space Station is in full operation. The advantages of a permanent space station, already demonstrated by the Russian Mir station, are continuous availability of expert crew and a wide range of equipment, possibility of long-term experiments where this is waranted, increased numbers of subjects through larger laboratory space, proper controls in the large 1-G centrifuge, easier repeatability of experiments when needed.
The limited number of flight opportunities during recent years probably explains why it has taken so long to acquire a sufficient number of high quality contributions for this seventh volume of Advances in Space Biology and Medicine. While initially the series wassailed at annually appearing volumes, we are now down to a biannual appearance. Hopefully, it will be possible to return to annual volumes in the future when results from space station experimentation at beginning to pour in.
The first three chapters of this volume deal with muscle. Fejtek and Wassersug provide a survey of all studies on muscle of rodents flown in space, and include an interesting demography of this aspect of space research. Riley reviews our current knowledge of the effects of long-term spaceflight and re-entry on skeletal muscle, and considers the questions still to be answered before we can be satisfied that long-term space missions, such as on the space station, can be safely undertaken. Stein reviews our understanding of the nutritional and hormonal aspects of muscle loss in spaceflight, and concludes that the protein loss in space could be deleterious to health during flight and after return. Strollo summarizes our understanding of the major endocrine systems on the ground, then considers what we know about their functioning in space, concluding that there is much to be learned about the changes taking place during spaceflight. The many problems of providing life support (oxygen regeneration and food supply) during extended stay on the Moon, on Mars, or in space by means of plant cultivation are discussed by Salisbury. The challenges of utilizing electrophoresis in microgravity for the separation of cells and proteins are illustrated and explained by Bauer and colleagues. Finally, the chapter on teaching of space life sciences by Schmitt shows that this field of science has come of age, but also that its multidisciplinary character poses interesting challenges to teaching it.

This fourth volume in the series, dedicated entirely to the results of the first European study of the effects of long-term confinement and isolation. The volume continues to attempt to fulfill the aim of this series, to bring the findings and accomplishments in the field of space biology and medicine to a wider group of scientists than merely the relatively small group of biologists and physiologists currently involved in space experimentation.
The contributions are not only nicely spread geographically with three chapters from the United States, two each from Russia, Europe, and Japan, they also offer a wide range of topics in the field, covering humans, animals, plants, cells, and even potential extraterrestrial beings.
As before, not only problems investigated and results obtained are reviewed, but also some of the technical aspects peculiar to this field are treated. An example in this volume is the chapter on virtual environments by Ellis, which is meant to help investigators understand the opportunities that these techniques might offer for future investigations.
In view of the limitations on flight opportunities and the constraints still inherent in orbital experimentation, it is also important to consider the information that can be obtained from studies on the ground. In addition to simulation studies like bed rest for human subjects (see the chapter by Edgerton et al. on neuromuscular adaptation), tail suspension of rats, and plants on a clinostat (see the chapter by Masuda et al.), there is the interesting possibility of using gravitropic mutants for studying the effects of weightlessness on plant growth as described by Takahashi and Suge.
Two chapters are devoted to a review of the results on rats flown on nine Cosmos biosatellite flights between 1973 and 1989: the chapter by Krasnow deals with the neuromorphological effects of micro- and hypergravity; that by Popova and Grigoriev with the metabolic effects of spaceflight. The effects of weightlessness on heart and lung function in humans are reviewed in detail by Bonde-Petersen and Linnarson.
While the study of humans, animals, and plants in spaceflight have taught us much about the effects of the space environment on living organisms, we still have a very limited understanding of the mechanisms operating in these effects. The chapter by Rijken et al. on the effects of gravity on the cellular response to epidermal growth factor demonstrates how, by a judicious use of experiments on the ground and in sounding rockets, the mechanism of a microgravity effect on cell growth could be unravelled.
The question whether there is intelligent life elsewhere in the universe has intrigued mankind for a long time. In the chapter by Coulter et al. on NASA's High Resolution Microwave Survey the project to search for the existence of such life is described. The postscript to this chapter tells how through an unfortunate decision of the U.S. Congress this project after a successful start is threatened with an untimely ending.