Volume 10 of Advances in Disease Vector Research consists of seven chapters on vectors that affect human or animal health and six chapters on plant pathogens and their vectors. In Chapter 1, Yasuo Chinzei and DeMar Taylor discuss hormonal regulation of vitellogenesis in ticks. Many blood sucking insects and ticks transmit pathogens by engorgement, which induces vitellogenesis and oviposition in adult animals. To investigate the pathogen transmission mechanism in vector animals, information on the host physiological and endocrinological conditions after engorgement is useful and important because pathogen development or proliferation occurs in the vector hosts at the same time as the host reproduction. Chinzei and Taylor have shown that in ticks, juvenile hormone (JH) is not involved in the endocrinological processes inducing vitellogenin biosynthesis. Synganglion (tick brain) factor(s) (vitellogenesis inducing factor, VIF) is more important to initiate vitellogenesis after engorgement, and ecdysteroids are also related to induction of vitellogenin synthesis. In their chapter, based mainly on their own experimental data, the authors discuss the characterization of main yolk protein, vitellogenin (Vg) , biosynthesis and processing in the fat body, and hormonal regulation of Vg synthesis in tick systems, including ixodid and argasid ticks.

Ecological Land Classification (ELC) refers to the description of land resources at a range of spatial resolutions (i.e. global to local) and for a range of purposes or values. The emerging science of ELC is in fact a very carefully integrated blend of vegetation and earth sciences, climatology, cartography and ecology with a range of new technologies and methodologies including computer-based geographic information systems, remote sensing and simulation modelling. This publication defines the current state-of-the-art' of ELC. It provides particular insight into the role of ELC in current and future forest resource planning and management, and emphasizes its application and usefulness at various spatial scales, for a variety of geographic locations, and under a range of management scenarios/constraints. The book is an invaluable and substantial reference source about the current trends in ELC and will be of particular value to ecologists, foresters, geographers, resource managers, wildlife biologists, GIS and remote sensing specialists, educators and students.

Recently, there has been tremendous progress in the genetic transformation of agricultural crops, and plants resistant to insects, herbicides, and diseases have been produced, field tested and patented. "Transgenic Crops I" compiles this information on cereals, grasses, legumes, and oilseed crops. It is divided into two sections: I. Cereals and Grasses: wheat, rice, maize, barley, sorghum, pearl millet, triticale, "Agrostis" spp., "Cenchrus" "ciliaris," "Dactylis glomerata," "Festuca" "arundinacea," "Lolium" spp., and sugarcane. II. Legumes and Oilseed Crops: "Arachis hypogaea," "Brassica juncea," "Brassica" " napus," " Cicer arietinum," " Glycine" "max," " Gossypium" "hirsutum," " Helianthus annuus," "Lens culinaris," "Linum usitatissimum," "Sinapis alba," "Trifolium," and "Vicia" "narbonensis."
This book is of special interest to advanced students, teachers, and research workers in the field of plant breeding, genetics, molecular biology, plant tissue culture, and plant biotechnology in general.

The chapters in this book represent detailed versions of papers presented at the Symposium on Viral Genes and Plant Pathogenesis held at Lexington, Kentucky on October 16 and 17, 1989. In selecting topics and authors, we attempted to have represented a spectrum of systems which are at the forefront of research on plant virus genes and gene products, particularly as they relate to plant disease. The book also contains pertinent discussion of the papers presented at the symposium, as well as summaries, observations and projections of future research directions prepared by the session chairmen. We wish to express our appreciation to Dr. D. L. Davis, of the RI. Reynolds Tobacco Company for suggesting the organization of the Symposium and the publication of the proceedings, and to the R 1. Reynolds Tobacco Company for the financial support which made the symposium possible. We also wish to thank those of our colleagues in the Department of Plant Pathology, University of Kentucky, who very ably and in many ways contributed to the organization and conduct of the conference. Thomas P. Pirone lohnG. Shaw v Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi INDUCTION OF HOST GENES BY THE HYPERSENSITIVE RESPONSE OF TOBACCO TO VIRUS INFECTION J. F. Bol, C. M. A. van Rossum, Bl. C. Cornelissen and H. J. M. Linthorst . . . . . . . . . . . . . . . . . l COAT PROTEIN MEDIATED RESISTANCE IN TRANSGENIC PLANTS Roger N. Beachy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 STRUCTURE AND FUNCTIONS OF TOBACCO MOSAIC VIRUS RNA Yoshimi Okada, Tetsuo Meshi, and Yuichiro Watanabe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Heliothis ("Bull worm") species are one of the major pests of field crops worldwide, including sorghum, tomatoes, lettuce, and cotton. Pest problems have intensified over the years as the total area given to agricultural host plants has increased. This comprehensive text, written by experienced researchers, assembles biological and ecological research techniques and approaches to Heliothis management: from the fundamental question of defining genetic species to collecting, rearing, and sampling techniques for the construction of life tables; the measurement of predator impact and physiological development; the detection and measurement of behavior, migration, and diapause; population genetics and resistance. Approaches to modelling population dynamics are also explored. This book is intended for beginning research students as well as experienced workers. It will be a valuable reference for entomologists, population ecologists, and agronomists concerned with crop protection.

Soil is formed from the physical and chemical weathering of rocks-processes described historically becau'se they involve eons of time-by glaciation and by wind and water transport of soil materials, which are later deposited in deltas and loessial planes. Soil undergoes further transformations over time and provides a habitat for biological life and a base for the development of civilizations. Soil is dynamic-always changing as a result of the forces of nature and particularly by the influences of man. Soil has been studied as long as history has been documented. Numerous references to soil are found in historical writings such as Aristotle (384-322 Be), Theophrastus (372-286 Be), Cato the E1der (234-149 Be), and Varro (116-27 Be). Some of the earliest historical references have to do with the erosional forces of wind and water. The study of soils today has taken on increased importance because a rapidly expanding population is placing demands never before experienced on the soil. This has led to an increase in land degradation. Land degradation is one of the most severe problems facing mankind. Volume 11 of Advances in Soil Science was devoted entirely to this critical area of soil science. This series, Advances in Soil Science, was established to provide a forum for leading scientists to analyze and summarize the available scientific information on a subject, assessing its importance and identifying additional research needs.

This book is an outcome of a research project on "Sustainable Forestry and the Environment in Developing Countries". The project has been run by Metsantutki muslaitos METLA -the Finnish Forest Research Institute since 1987 and will be completed this year. A major output by this project has so far been a report in three volumes on "Deforestation or development in the Third World?" The purpose of our multidisciplinary research project is to generate new knowl edge about the causes of deforestation, its scenarios and consequences. More knowledge is needed for more effective, efficient and equitable public policy, both at the national and intemationallevels in supporting sustainable forestry in develop ing countries. Our project has specifically focused on 90 tropical countries as one group and on three subgroups by continents, as well as the three case study countries, the Philippines, Ethiopia and Chile. The University of Joensuu has been our active partner in the Philippine study. We have complemented the three cases by the analyzes of Brazil and Indonesia, the two largest tropical forest-owning countries. Some other interesting country studies were annexed to complement our book both by geography and expertise. The United Nations University, World Institute for Development Economics Research, UNUIWIDER in Helsinki Finland has also been partly engaged. Most of the results from its project on "The Forest in the South and North in Context of Global Warming" will, however, be published later in a separate book.

Soil is formed from the physical and chemical weathering of rocks-processes described historically because they involve eons of time-by glaciation, and by wind and water transport of soil materials, later deposited in deltas and loessial planes. Soil undergoes further transformations over time and provides a habitat for biological life and a base for the development of civilizations. Soil is dynamic - always changing as a result of the forces of nature and particularly by the influences of man. Soils have been studied as long as history has been documented. W. H. Gardner told of writings on clay tablets, dating about 1700 Be, in his review, "Early Soil Physics into the Mid-20th Century;' published in Volume 4 of this series. Those writings gave specific instructions on cultivating the soil and seeding crops. Numerous references to soil are found in historical writings, such as Aristotle (384-322 Be), Theophrastus (372-286 Be), Cato the Elder (234-149 Be), and Varro (116-27 Be). Some of the earliest historical refer ences to soil 3000 or more years ago have to do with erosional forces of wind and water. The study of soils today has taken on increased importance because a rapidly expanding population is placing demands on soil that has never before been experienced. Soil scientists have professionally divided themselves into separate disciplines-physics, chemistry, microbiology, mineralogy, genesis, and the like. Studies range from very basic to very applied, and to literally every corner of the earth, and ofthe moon as well."

The Conference on Tropical Rainforest Research: Current Issues was organised by the University of Brunei Darussalam and The Royal Geographical Society, London, and held in Bandar Seri Begawan, Brunei Darussalam, over 8 days in April 1993. Over 160 participants from 22 countries attended the Conference, which was opened on the 9th April by the Brunei Darussalam Minister for Home Affairs, Yang Berhormat Pehin Orang Kaya Laila Setia Bakti Diraja Dato Laila Utama Haji Awang Isa bin Datu Perdana Menteri Dato Laila Utama Haji Awang Ibrahim. The conference was initially intended to provide a forum to present the results of the expedition into the lowland mixed dipterocarp forest of the Temburong District of Brunei Darussalam, which had been jointly organised by the University of Brunei Darussalam and The Royal Geographical Society, London. The 15-month expedition, lasting from January 1991 to March 1992, was based at the then newly-completed Kuala Belalong Field Studies Centre, a research and education facility set up by the University with funds provided by the Brunei Government and Brunei-Shell Petroleum Sdn Bhd. The expedition, with over 70 scientists taking part, received financial support from a wide range of sponsors and Corporate Patrons, including Royal Brunei Airlines, the Baring Foundation, Daiwa-Dicam, Greencard Trust, the Hongkong Bank, Morgan Grenfell and Nomura-Nimco. The conference itself was supported by donations from Brunei-Shell Sdn Bhd, Royal Brunei Airlines and Standard Chartered Bank.

The study of soils has taken on increased importance because a rapidly expanding population is placing demands on the soil never before experi enced. This has led to an increase in land degradation. Land degradation is one of the most severe problems facing mankind. Volume 11 of Advances in Soil Science was devoted entirely to this critical area of soil science. The editors of that volume, R. Lal and B.A. Stewart, defined soil degradation as the decline in soil quality caused by its misuse by humans. They further stated that soil degradation is a major concern for at least two reasons. First, it undermines the productive capacity of an ecosystem. Second, it affects global climate through alterations in water and energy balances and disruptions in cycles of carbon, nitrogen, sulfur, and other elements. Through its impact on agricultural productivity and environment, soil deg radation leads to political and social instability, enhanced rate of deforesta tion, intensive use of marginal and fragile lands, accelerated runoff and soil erosion, pollution of natural waters, and emission of greenhouse gases into the atmosphere. In fact, soil degradation affects the very fabric of mankind."

On the understanding that few people ever read the preface to any book and also on the understanding that even those few people who do read the preface realize that virtually nothing of any substance is ever said, I shall write at such length as will be proportional to my expected readership. The meetings of the International Society on Oxygen Transport to Tissue provide a forum for discussion amongst scientists who, although being from very diverse and specialized backgrounds, have tissue oxygenation as a unifying theme of interest. The wide variety of research material presented in this volume and the multiplicity of the experimental techniques described, should serve as an adequate gauge to the range of expertise and knowledge of the society's members. Such diversity should also stress the importance of the need for multidisciplinary approaches to complex biological problems. In attempting a fundamental characterization of a biological process such as tissue oxygenation, the application of very many separate research skills are necessary, such as mathematics, engi neering, biophysics, biochemistry, physiology, histology and clini cal medicine. The success of the ISOTT has - and we hope - will con tinue to be causing a combination of individuals to direct their specialized knowledge to the many facets of a single proces- tissue oxygenation."

In the past 10 years, there has been a resurgence in interest in soil management and conservation of the soil resource. With the knowledge we have accumulated in the past 100 years, there is the possibility of developing new and innovative ways of effectively managing the soil. The emphasis on sustainable agriculture requires that we understand how to utilize the soil as a viable living resource. To meet the world demand for food within the next 50 years requires a healthy and strong soil resource which can sustain production. With the dedication of the National Soil Tilth Laboratory in 1989, it was decided that one contribution the laboratory could make to agri cultural science would be to foster an exchange of information on soil management. The focus of that interchange centers on long-term soil management. If we are to fulfill the goals of sustainable agriculture, environmental quality, and feeding the world, there will have to be an increased understanding of how to effectively manage the soil. Long-term soil management requires integrated and interdisciplinary research to bring all of the information together in terms which would be applicable to all soils. To accomplish this goal a workshop is held each year, with the exchange of information focusing on a single topic within the framework of developing effective strategies for long-term soil management. With the forum to focus on an individual theme each year, the theme for the initial workshop was "Limitations to Plant Root Growth."

The world needs for food and fiber continue to increase. Population growth in the developing countries peaked at 2. 4 percent a year in 1965 and has fallen to about 2. I percent. However, in many developing countries almost half the people are under 15 years of age, poised to enter their productive and reproductive years. The challenges to produce enough food for this growing population will remain great. Even more challenging is growing the food in the areas of greatest need. Presently the world has great surpluses of food and fiber in some areas while there are devastating deficiencies in other areas. Economic conditions and the lack of suitable infrastructure for distribution all too often limit the alleviation of hunger even when there are adequate supplies, sometimes even within the country itself. World hunger can only be solved in the long run by increasing crop production in the areas where the population is growing most rapidly. This will require increased efforts of both the developed and developing countries. Much of the technology that is so successful for crop production in the developed countries cannot be utilized directly in the developing countries. Many of the principles, however, can and must be adapted to the conditions, both physical and economic, of the developing countries. This series, Advances in Soil Science.

Providing a link between theoretical and applied aspects of plant nutrition and agriculture, this book introduces new concepts in plant nutrition. It shows how these can be applied in order to assess the nitrogen status in crops and to improve nitrogen nutrition through optimized N fertilization management. In this way economic benefits can be obtained, while at the same time preventing detrimental effects on the environment. The main agricultural crops - grasses, wheat, barley, Durum wheat, maize, sorghum, grain legumes and potatoes - are covered. The book will be an invaluable source for agronomists.

A knowledge of forest site and forest productivity variables is fundamental to sound forest practice everywhere. The ability to identify sites and site problems correctly and manipulate productivity variables for maintenance or improvement of productivity is the basis of modern forest management. Although the basic facts regarding forest site and productivity apply throughout the world, the application of information and the response to manipulation vary greatly and depend on local forest conditions. The September 1981 World Congress of the International Union of Forest Research Organizations (IUFRO) in Kyoto, Japan was the occasion for the special meeting on Forest Site and Productivity sponsored by the IUFRO Site Group Sl.02. This meeting brought together forest site and productivity researchers from across the world to review current thought and the state of site research. Information not ordinarily available in one place was presented at this meeting. As organizer of the session, I decided to attempt to publish the papers in one volume. Arrangements were made with a publisher, Martinus Nijhoff, and also with the authors. The process of publication has taken longer than desirable, but the volume does appear at an opportune time coincident with the 1986 IUFRO World Congress in Yugoslavia. Material contained in this publication will set the stage for Site Group discussions at the 1986 meeting. This volume assembles the thought of forest research workers from many different countries and therefore many different kinds of forests.

"Reviews of Environmental Contamination and " "Toxicology"contains timely review articles concerned with all aspects of chemical contaminants (including pesticides) in the total environment, including toxicological considerations and consequences. It attempts to provide concise, critical reviews of advances, philosophy, and significant areas of accomplished or needed endeavor in the total field of residues of these and other foreign chemicals in any segment of the environment, as well as toxicological implications.

DEVELOPMENT AND DISTURBANCE IN AMAZON FORESTS Contrasting Impressions 6 2 The rain forests of the Amazon Basin cover approximately 5.8 x 10 km (Salati and Vose 1984). Flying over even just part of this basin, one gazes hour after hour upon this seemingly infinite blanket of green. The impression of immen sity is similar when viewed from the Amazon River itself, or from its tributar ies. From a hammock on the shaded deck of a riverboat, the immensity of the forest presents an incredible monotony as one view of the shoreline blends unnoticeably into another. From both perspectives, the overwhelming reaction to the sea of trees that stretches from horizon to horizon is a sense of the vastness of the rain forest. In September 1985, I got a different impression of the rain forest. Several students and I journeyed in a self-propelled car along the single-track railroad that stretches almost 1000 km from the Carajas iron ore mine in the rain forest of Para State, Brazil, all the way to Sao Luis on the coast (Fig. 1.1)."

The key to sustaining the soil resource base is to maintain, or enhance, soil quality. Soil quality cannot be seen or measured directly from the soil alone but is inferred from soil characteristics and soil behavior under defined conditions. In essence, the quality of soils is analogous to the health of humans, and just as there is no single characteristic that can be measured to quantify a person's health, there is no single measurement that can quantify soil quality. However, there are certain characteristics, particularly when considered together, that are good indicators. Soil quality, just as human health, can be maintained or enhanced by good management practices; and seriously degraded-sometimes irrevers ibly-with poor practices. Soil quality is also important because it has direct and indirect effects on air quality and water quality. While the enhancement of soil quality does not always assure parallel improvements in the quality of air and, particularly, water resources, this is often the case. However, soil deg radation is invariably accompanied by degraded qualities of both air and water resources. The consensus among many scientists is that the greatest challenge is not increasing production, but preventing serious deterioration of the soil and water resource base so that the production level can be sustained."

"Reviews of Environmental Contamination and Toxicology" contains timely review articles concerned with all aspects of chemical contaminants (including pesticides) in the total environment, including toxiological considerations and consequences. It attempts to provide concise, critical reviews of advances, philosophy, and significant areas of accomplished or needed endeavor in the total field of residues of these and other foreign chemicals in any segment of the environment, as well as toxicological implications.

Progress in wood chemistry has been related mainly to chemical wood pulping and bleaching and chemical utilization of wood and wood extractives. Meth ods of wood analysis were developed by Schorger (proximate analysis in 1917) and Dore (summative analysis in 1919), and standard methods based on Schorger's method, e.g., TAPPI standards (Technical Association of the Pulp and Paper Industry), have been widely used for chemical analysis of woods in many countries. Thus it is generally known that wood is composed of about 50% cellulose, 20-35% of lignin, 15-25% of hemicelluloses, and variable amounts of extractives. Chemical characterization and efficient utilization of these wood components have been studied in laboratories of wood chemistry and technology in universities and government institutions. In the last decade, biochemistry and molecular biology of microorganisms, animals, and plants have greatly progressed. At the same time wood has been recognized as a unique renewable ecomaterial produced by trees using solar energy. In addition, many desirable properties of wood and wood components as biomaterial that affects physiology and psychology in humans have recently attracted attention."

PH. BOURDEAU Directorate-General Science. Research and Development. Commission of the European Communities. Brussels. Belgium We are living on a unique planet, the only one in the solar system where life exists. The very existence of life has modified the physical and chemical environment of the earth, its atmosphere and oceans, in a way that makes life sustainable. This system with its complex cybernetic mechanisms has been named GAIA by Lovelock. Man has always interfered with it on a more or less limited scale. This interference is now reaching global proportions such as climate modifications resulting from CO and trace gas 2 accumulation in the atmosphere or the destruction of stratospheric ozone, not to speak of global radioactive contamination. GAIA will probably prevail as a living system but it probably does not give much importance to man's survival as such, and it is man that has to take care of his own survival. In the ecosystem of Planet Earth, soils are the thin interface between lithosphere and atmosphere which constitutes the essential substrate for the terrestrial biosphere, the productivity of which far exceeds that of the oceans, even though the latter cover a much larger area than the continents. Soils themselves are complex systems. They develop through weathering of minerals, are colonised by living organisms which in turn modify their substrate making it suitable for other organisms. This induces a primary ecological succession which eventually reaches a climax, in equilibrium between climate, soil and the biological communities.

The study of soils today has taken on increased importance because a rapidly expanding population is placing demands on the soil never before experienced. This has led to an increase in land degradation. Land degradation is one of the most severe problems facing mankind. Volume 11 of Advances in Soil Science was devoted entirely to this critical area of soil science. From the beginning of agriculture until about 1950, increased food production came almost entirely from expanding the cropland base. Since 1950, however, the yield per unit of land area for major crops has increased dramatically. Much of the increase in yields was because of increased inputs of energy. Between 1950 and 1985, the farm tractor fleet quadrupled, world irrigated area tripled, and use of fertilizer increased ninefold. Between 1950 and 1985, the total energy used in world agriculture increased 6. 9 times. Until recently, sustainability was seldom, if ever, mentioned in agricultural literature. Now, it is one of the most widely used terms. The high costs ofirriga tion development, escalating energy costs during the 1970s, public concern over potential negative impacts of fertilizer and pesticides on water supplies, soil ero sion, soil compaction and salinity problems, and other concerns have caused many people to question whether many of the present agriculture systems can be sustained. As a result, soil science is beginning to focus more on sustaining the resource base."

In analysing the development and achievements of Polish forestry and forest industries over the last four decades, it is necessary to take into consideration the situation prevailing after the end of the Second World War, when these sectors of the national economy were starting their activities. First of all, it is necessary to consider the effects of the war such as: (a) the harvesting from the forests of the present Polish territory of 3 about 200 million m of merchantable wood, which is equal to the normal harvest over a l2-year period; (b) the destruction of over half the woodworking industrial potential. In consequence, the forested area inside the new Polish boundaries amounted 40 years ago only to 20.8 per cent of the whole area of the country. There has been a continuing process of increasing the forested area of the country (although at a diminishing rate). In 1986 the forest area amounted to 27.7 per cent of the land surface, that is to 8.7 million ha, an increase of over 2 million ha in 40 years. Intensive afforestation, performed regardless of the ownership category of the land by the State forest service, was aimed primarily at making good the losses in the forested area and the rational use of land not fit for agricultural purposes.

Energy and agriculture are both extremely broad subjects and their interactions - the subject of this book - cover almost the full spectrum of the agricultural sciences. Yet the subject is a relatively new one whose importance first received widespread recognition barely a decade ago, following the dramatic increase in oil prices during 1973. The impact of this increase was such as to promote a world-wide debate on the future direction that agriculture should take. This debate was, and is, of particular concern in countries where agriculture plays a leading role in economic and social development. During the last half century many national agricultural systems have been transformed from almost closed, self-sufficient systems with few locally produced inputs geared to satisfy local requirements, to intensive, open systems, utilizing large quantities of energy-rich inputs such as fossil fuel for manufactured agro-chemicals, water distribution and imported animal feedstuffs to produce a range of sophisticated products, often for export, which in tum require many energy-rich inputs for their marketing. This industrialization of agriculture has proved to be very successful in many respects and indeed was accepted as a general model for agricultural development allowing increased productivity and efficiency per unit land, labor and water, even in areas with limited natural resources.

An extraordinary development of the knowledge, concepts and biomedical applications has occurred during the past two decades in the biological sciences, including the Reticuloendothelial Sys- tem (RES). For example, it is now widely recognized that distinct classes of cells are involved in the recognition of "exogenous" invaders of the body such as microorganisms and other foreign an- tigens, as well as of "endogenous" parasites represented by trans- formed neoplastic cells and altered "self" antigens. Prominent among cell populations involved in such recognition of antigens and subsequent immune responses are those constituting the RES. In recent years, there has been much discussion and indeed contro- versy as to what constitutes such a system and even whether the term "RES" is appropriate. Some investigators feel that the phago- cytes are the most important cells of the RES as they playa major role in the defense mechanism of the host. Mononuclear phagocytes include tissue macrophages ~s well as circulating monocytes and their precursors. Although phagocytosis is a major functional ac- tivity, it is only one of their several functions. The important role of phagocytes and other mononuclear cells in antibody forma- tion, cell-mediated immunity, specific and non-specific resistance to microorganisms and tumor cells, as well as homeostatic adjust- ments in general has become the focus of attention for many inves- tigators.