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Ubiquitination is a post-translational modification that affects protein degradation as well as a variety of cellular processes. Methods that globally profile ubiquitination are powerful tools to better understand these processes. Here we describe an updated method for identification and quantification of thousands of sites of ubiquitination from cells, tissues, or other biological materials. The method involves cell lysis and digestion to peptides, immunoaffinity enrichment with an antibody recognizing di-glycine remnants left behind at ubiquitinated lysines, and liquid chromatography-tandem mass spectrometry analysis of the enriched peptides.

Bench-to-bedside axis of therapeutic product development is currently being oriented towards minimum invasiveness on both ends-not only clinical application but harvesting of the starting biological material as well. This is particularly relevant for Advanced Therapy Medicinal Products and their specific legislative requirements, even more so in skin regeneration. It is precisely the skin equivalents and grafts that benefit from the minimum-to-noninvasive approach to a noteworthy extent, taking in account the sensitive nature of both skin harvesting and grafting.This chapter includes protocols for two separate steps of generating skin equivalent from the cells cultured from hair follicle outer root sheath. The first step is a non-pigmented epidermal equivalent generated from human keratinocytes from the outer root sheath named non-pigmented epidermal graft. The second step consists of co-cultivating human keratinocytes and human melanocytes from the outer root sheath, hereby producing a pigmented epidermal graft.

Keratins, as a group of insoluble and filament-forming proteins, mainly exist in certain epithelial cells of vertebrates. Keratinous materials are made up of cells filled with keratins, while they are the toughest biological materials such as the human hair, wool and horns of mammals and feathers, claws, and beaks of birds and reptiles which usually used for protection, defense, hunting and as armor. They generally exhibit a sophisticated hierarchical structure ranging from nanoscale to centimeter-scale: polypeptide chain structures, intermediated filaments/matrix structures, and lamellar structures. Therefore, more and more attention has been paid to the investigation of the relationship between structure and properties of keratins, and a series of biomimetic materials based on keratin came into being. In this chapter, we mainly introduce the hierarchical structure, the secondary structure, and the molecular structure of keratins, including α- and β-keratin, to promote the development of novel keratin-based biomimetic materials designs.

Cryopreservation as a method that enables long-term storage of biological material has long been used for the conservation of valuable zebrafish genetic resources. However, currently, only spermatozoa of zebrafish can be successfully cryopreserved, while protocols for cryopreservation of eggs and embryos have not yet been fully developed. Transplantation of germline stem cells (GSCs) has risen as a favorable method that can bypass the current problem in cryopreservation of female genetic resources and can lead to reconstitution of fish species and lines through surrogate production. Here, we describe essential steps needed for the cryopreservation of spermatogonial stem cells (SSCs) and their utilization in the conservation of zebrafish genetic resources through SSC transplantation and surrogate production.

Pseudopotamilla occelata is a polychaete worm distributed widely in the northern part of the Pacific coast, having value as fishing bait as well as biological material for some basic research areas, including reproduction. Here we describe methods for handling the gametes and embryos of this worm, focusing on such topics as maintenance of adults, induction of oocyte maturation and fertilization, culture of embryos and larvae, microinjection into oocytes, and calcium (Ca2+) imaging.

Bioprinting has emerged as a promising method for precise spatiotemporal patterning of biological materials such as living cells, genetic materials, and proteins, which are sensitive to any other fabrication techniques. Bioprinting allows the generation of tissue constructs and models that closely mimic the anatomical and physiological attributes of a chosen tissue. In vitro toxicology assays can greatly benefit from bioprinting as drugs can be screened with higher efficiencies in a significantly reduced period. This protocol describes a method for fabricating bioprinted cartilage constructs which can be used for in vitro toxicology studies employing a scalable "tissue strand" bioprinting modality.

Laser microdissection (LMD) technology has been widely applied to plant tissues, offering novel information on the role of different cell-type populations during plant-microbe interactions. In this chapter, protocols to apply the LMD approach to study plant and fungal transcript profiles in different cell-type populations from arbuscular mycorrhizal (AM) roots are described in detail, starting from the biological material preparation to gene expression analyses by RT-PCR and RT-qPCR.

Purpose To explore the efficacy and safety of prophylactic temporary balloon occlusion of the infrarenal abdominal aorta during caesarean for the management of patients with placenta praevia accreta. Methods Two hundred and sixty-eight cases of placenta praevia accreta from January 2012 to June 2015 were retrospectively reviewed. Group A included two hundred and thirty patients who underwent prophylactic temporary balloon occlusion of infrarenal abdominal aorta followed by caesarean section. Group B included thirty-eight patients who underwent caesarean without endovascular intervention. The parameters including operating room time, estimated blood loss, blood transfusion volume, PT (prothrombin time) during operation, days in the intensive care unit, and total hospital days were compared between the two groups. Results The operating room time, estimated blood loss, PT, the incidence of hysterectomy, blood transfusion volume, postpartum haemorrhage, and days in intensive care unit were lower in group A than in group B, with statistical significance (P 0.05). No patient in the group with prophylactic temporary balloon occlusion of the infrarenal abdominal aorta was performed hysterectomy, while three patients in group B were performed hysterectomy because of uncontrollable haemorrhage. Conclusions The results indicate that prophylactic temporary balloon occlusion of infrarenal abdominal aorta followed by caesarean section is safe and effective to control intraoperative blood loss and greatly decreases the risk of hysterectomy in patients with placenta praevia accreta.

A capacitive sensor was proposed and tested for the monitoring and control of a freeze drying process of a vaccine against the Newcastle disease of birds. The residual moisture of the vaccine was measured by the thermogravimetric method. The vaccine activity was determined by titration in chicken embryos. It was shown that, at the stages of freezing and primary drying, a capacitive sensor measured the fraction of unfrozen liquid phase in a material and allowed one to control the sublimation stage of drying in an optimal way. This prevented the foaming of the material and shortened the total drying time approximately twice. The control range at the sublimation stage of drying expanded up to −70°C. It was found at the final stage of drying that the signal of a capacitive sensor passed through a maximum value. We supposed that this maximum corresponds to the minimum of intramolecular mobility of biological macromolecules and hence to the optimal residual moisture of the material, which ensures long-term preservation of its activity. We also suppose that using the capacitive sensor at the final stage of drying allows one to more precisely detect the time when the residual moisture of dried material reaches the optimal value.

When we want to design, that is, prepare a drawing and fabricate something to replace a desired body part or malfunctioning organ(s) due to disease processes, trauma, or surgical removal, it is necessary to understand the real nature and biomechanical characteristics of those anatomical parts, e.g., tissues and organs. Anthropometry is the science and practice of measuring the size and shape of the human body and its parts. To measure the properties of biological materials and tissues are also anthropometry’s tasks. Biomechanics, in turn, studies the structure and function of biological systems using the methods of mechanics. The composition and behavior of bones, cartilages, and ligaments have been studied for many years. However, although we know much about these tissues, newer and better measurement techniques continuously improve the available data. It should be remembered that there are biological variations and environmental factors that significantly affect the mechanical properties of biological tissues.

Hybrid biomimetic nanosensors use selective polymeric and biological materials that integrate flexible recognition moieties with nanometer size transducers. These sensors have the potential to offer the building blocks for a universal sensing platform. Their vast range of chemistries and high conformational flexibility present both a problem and an opportunity. Nonetheless, it has been shown that oligopeptide aptamers from sequenced genes can be robust substrates for the selective recognition of specific chemical species. Here we present first principles molecular modeling approaches tailored to peptide sequences suitable for the selective discrimination of small molecules on nanowire arrays. The modeling strategy is fully atomistic. The excellent performance of these sensors, their potential biocompatibility combined with advanced mechanistic modeling studies, could potentially lead to applications such as: unobtrusive implantable medical sensors for disease diagnostics, light weight multi-purpose sensing devices for aerospace applications, ubiquitous environmental monitoring devices in urban and rural areas, and inexpensive smart packaging materials for active in-situ food safety labeling.

New medical technologies provide us with new possibilities in health care and health care research. Depending on their degree of novelty, they may as well present us with a whole range of unforeseen normative challenges. Partly, this is due to a lack of appropriate norms to perceive and handle new technologies. This chapter investigates our ways of establishing such norms. We argue that in this respect analogies have at least two normative functions: they inform both our understanding and our conduct. Furthermore, as these functions are intertwined and can blur moral debates, a functional investigation of analogies can be a fruitful part of ethical analysis. We argue that although analogies can be conservative, they are nevertheless useful because they bring old concepts to bear upon new ones. We also argue that there are at least three ways in which analogies can be used in a creative manner. First, understandings of new technologies are quite different from the analogies that established them, and come to be analogies themselves. That is, the concepts may turn out to be quite different from the analogies that established them. Second, analogies transpose similarities from one area into another, where they previously had no bearing. Third, analogies tend to have a figurative function, bringing in something new and different from the content of the analogies.

The main methods of immobilization employed to stabilize the life time of photosynthetic material are studied. Various parameters and properties concerning the immobilization procedures are evaluated: method, biological material, techniques to measure the photosynthetic activity, storage and operational stabilities. A comparison between two methods of immobilization (chemical and physical) to measure the effect of herbicides which inhibited photosynthesis is discussed. The practical implication of photosystem II is emphasized.

We need only to consider our own bodies as an example to realize the complexity of biological material. Our body is three-dimensional and composed primarily of light elements, most of which are organized into a mixture of periodic and aperiodic structures. These structures range from simple molecules and macromolecules to complex heteropolymers, all bathed in an aqueous solution of ions and electrolytes. We are thermodynamically unstable, live at ambient temperatures and pressures, and are sensitive to ionizing radiation.

One of the major reasons for pursuing the chemical structure of the biological material known as slow-reacting substance of anaphylaxis (SRS-A) was that this material was known to be a potent bronchoconstrictor substance in guinea pigs [1] and in isolated human airways [2]. Thirty years ago, the simple concept was that SRS-A was released from sensitized cells following antigen sensitization and challenge, and that the released material transduced a signal at an as yet to be identified receptor leading to smooth muscle constriction and therefore the manifestations of human asthmA. It has been almost 25 years since the elucidation of the structure of SRS-A as a mixture of the cysteinyl leukotrienes (LT) [3] and just over 5 years since agents that act on leukotriene pathway have been available as asthma treatments [4,5]. What have we learned about asthma from the use of these agents and what is the role of these agents in the treatment of asthma?

Biosynthetic reactions produce large amounts of PPi, as shown by the calculations presented in the chapter 1.2. However, most authors of biochemical textbooks assume that very little of it exists in living cells, because it is hydrolysed immediately by PPase. This assumption is logical, for the removal of PPi prevents the seemingly futile loss of energy which would take place, if the biosynthetic reactions would go backwards in the presence of PPi. However, in the past fifty years PPi has been shown to exist throughout the living world. In this chapter I shall discuss these studies beginning from bacteria and going via lower eukaryotes and plants to animals and humans.

The threat of attack on military and civilian targets with chemical and biological weapons is a growing national concern. The Defense Advanced Research Projects Agency (DARPA) is developing technologies for detecting biological materials in the natural environment. While several technologies show promise as broadband detectors, there is no “silver bullet” that detects all chemical and biological materials at the requisite levels of sensitivity and specificity. DARPA is developing a systems approach whereby several different advanced detection schemes (based on different physical phenomena) are being integrated into a biological detection suite.

Simple, rapid and cost-effective testing procedures were developed over the last few years, mainly for application in routine toxicity screening. One of the most significant breakthroughs in this regard are the highly standardized Toxkit microbiotests, which make use of dormant or immobilized stages of selected invertebrate species as the biological material from which the test species can be obtained. Toxkits can lso be used for "Fluotox" bioassays, in which sublethal (enzymatic) effects are detected after only one hour of exposure to toxicants. The prerequisite for the use of Fluotox tests as (rapid) alternatives to acute toxicity tests is a good correlation of the results of the former with those of the latter. The present study deals with the comparison of 24h toxicity tests performed with 2 Toxkit microbiotests (Artoxkit M™ and Thamnotoxkit F™) and the conventional Daphnia magna assay, with 1h Fluotox tests on the same species.

Biological effects of extremely low frequency (ELF) electromagnetic fields (EMF) demonstrated over the past few decades have proven notoriously difficult to replicate. There are many possible reasons for this problem: variations in exposure parameters; variations in biological material; variations in biological experimental protocols; or as some critics assume, lack of existence of any real effect in the original experiment. Until recently there have been very few attempts to conduct replication experiments.

Nuclear magnetic resonance (NMR) has been shown to be an invaluable tool in many fields of science for the non-destructive chemical analysis of samples. Solid-state NMR (SSNMR) with the use of magic angle spinning (MAS) has extended this powerful technique to samples that are not in solution. MAS utilizes fast mechanical rotation about an axis, at an angle of 54° 44’ with the external magnetic field. This technique has currently been used to analyze the chemical content and organization in a variety of biological materials.(1–6)

The mammalian cell-surface mono-ADP-ribosyltransferase, known as RT6 in the rat in which it was first uncovered (1-3), presents us with a common problem in modern biology, namely the definition of function in a molecule found by biochemistry (in which I include serology) and not by genetics. First detected as a so-called “polymorphic marker” by classical serological investigations, it immediately joined the queue, hugely extended a little later by the advent of monoclonal antibody technology, of functionally undefined cell surface molecules whose primary interest lay at that time in their utility either as cell subset or genetic markers. It was always important to ask functional questions about markers, rather than accept that they were basically flags established for the convenience of immunologists, but the tools to do so have only gradually become available. Most of these tools have now been applied to RT6, and so far, with great respect to all who have been involved in the enterprise, the functional identity of RT6 remains enigmatic. It would have been much easier had RT6 originally turned up as a functional defect: in this sense genetics is a better approach to analyse the complexity of biological material than biochemistry. However even genetics fails when the function of interest is specified by redundant genes, unless it happens that they are very close together and disappear together in a single deletion. Since the modern analytic is to do the genetics last and one gene at a time, mouse RT6 is about to be knocked out, but we must be prepared for an initial disappointment if neither of the two mouse genes Rt6-1 and Rt6-2 alone carries the functional burden.

The potential of pulsed neutron diffraction in structural determination of biological materials is discussed. The problems and potential solutions in this area are outlined, with reference to both current and future sources and instrumentation. The importance of developing instrumentation on pulsed sources in emphasised, with reference to the likelihood of future expansion in this area. The possibilities and limitations of single crystal, fiber and powder diffraction in this area are assessed.

Over the last few decades the use of biological materials in different fields of modern technology has grown rapidly. Examples are the widespread use of enzymes for stereospecific biosynthesis of materials and gene technological production of biologically important macromolecules.

The traditional method for the detection of nucleic acid sequences on membranes and in situ utilises radiolabelled compounds. These systems are still widely used in many applications, particularly where sensitivity and robustness are required1. However, in many situations there is less need for sensitivity and a more overriding need for resolution and speed of detection. To this end, effort has gone into the production and design of good, reliable, non-radioactive alternatives. Originally, these systems utilised hapten molecules, attached to nucleotides, to label the probes that were used to detect the presence of specific nucleic acid sequences. These hapten molecules were then detected through antibody conjugates. These too are now widely used in a number of applications2. In the field of chromosome in situ hybridization, detection through fluorescence labelled antibodies found great favour due to the ease of detection with modern microscopes and camera systems and, particularly with chromosome analysis, due to the low level of associated background fluorescence.

Indolic compounds can act as potent radical scavengers, a finding which has been particularly well studied in the case of melatonin and which has led to the conclusion that this function may be of physiological relevance, in addition to the roles of indolecamines in signaling (Reiter et al., 1993, 1994; Hardeland etal., 1993; Hardeland and Rodriguez, 1995). Among substances which are capable of terminating radical reaction chains, melatonin is the most efficient hydroxyl radical scavenger found to date in biological material (Tan et al., 1993). Along with the observation that melatonin accumulates in nuclei of various cell types (Menendez-Pelaez et al., 1993; Menendez-Pelaez and Reiter, 1993), this property suggests a protective role at DNA level.

The dielectric properties of biological materials are a measure of their interaction with electromagnetic fields. When people are exposed to non-ionizing radiation, such interactions take place in the human body at various levels of organization and may initiate biological responses. While these biological effects may or may not be desirable, they should, however, be well understood for safety regulation purposes and in order to exploit beneficial effects to their full potential. Dielectric spectroscopy, or the study of the frequency dependence of the dielectric properties, helps elucidate such mechanisms of interaction at the cellular and molecular level. This subject has been widely reviewed.1,2

Capillary electrophoresis (CE) is now one of the most efficient separation techniques. It has been rapidly developed since Jorgenson et al.1 used small diameter capillaries for the separation of ions in an electrical field. One of the greatest advantages of CE is the use of small sample amounts — from some few nl of sample to the cytosolic fluid of single cells2. These small sample volumes make it possible to solve a number of biological and clinical problems, where the amount of biological material is limited.

The interruption of the cooking process with a refrigerated storage period was studied for its effects on the texture kinetics of potatoes, green beans, carrots and apples. For potatoes a statistically significant effect on the texture was found. The inherently high variability of biological material makes that it is very difficult to use these effects in practical applications. In view of process design for cook-chill foods it is not necessary to take an interruption effect into account in texture models.

Perhaps because α-amylase is ubiquitous in all living systems, several natural inhibitors against this enzyme are found in biological materials. These inhibitors include the microbial nitrogen-containing carbohydrates with an oligobioamine unit, the microbial polypeptides such as Paim and Haim, and the larger protein inhibitors, found in cereals, legumes and some other higher plants. The protein inhibitors were discovered as early as 1933; however, much of the research has been performed since the mid 1970s, with important medical, nutritional and insect-control implications. The structures of several of the microbial N-containing carbohydrates and microbial polypeptides are known, and aminoacid sequences are also known for some of the higher plant protein inhibitors. Enzyme specificity studies with several α-amylases have been carried out, some detailed kinetic studies are available and a few chemical modification studies have been performed. Nevertheless, very little is known about why and how the compounds inhibit α-amylases, primarily those from animals and insects.

Physiological studies conducted over the last half century have established a role for hormones in virtually every aspect of plant development. Most of the pioneering work on hormone action used approaches that involve exogenous application of a hormone or inhibitor. There are severe limitations to what we can learn in this manner. Exogenous application of any biological material is subject to limitations of uptake, transport, sequestration and metabolism. Further, it is difficult to quantitate the amount of active material within the target tissue. For these reasons, it has been generally difficult to establish a direct relationship between a hormone and a particular developmental process.

The ability to introduce DNA into cells has been a sine-gua-non for the developments in molecular biology. One of the most unusual and unexpected technological breakthroughs in this arena is biolistic transformation. This technique goes under several names, including microparticle injection, gene gun, particle bombardment, etc. The basic idea, as originally conceived of by Sanford and coworkers (1), is disarmingly simple. DNA or other biological material is coated onto heavy metal microprojectiles and the microprojectiles are shot into the target cells, carrying the DNA in with them.

A Fuji imaging plate and synchrotron radiation are the most distinct innovations of the last twenty years in the X-ray diffraction experiments on biological materials. Here we present results of recent experiments on skeletal muscles made at Photon Factory, Tsukuba.

The first clinical trials of NCT were initiated at Brookhaven in 1951, using the Brookhaven Graphite Research Reactor (BGRR). Subsequently, the Brookhaven Medical Research Reactor (BMRR) was built primarily for clinical applications of NCT, with an improved beam extraction facility providing flexibility for future development of filters/moderators for NCT. This flexibility was exploited to provide an optimized epithermal neutron beam which was recently installed and tested in the east irradiation facility (shutter) of the BMRR.

Biosensor development continues to receive wide attention from researchers in the biomedical and biotechnology communities. The sustained level of interest in biosensors is due to the steady and marked evolution in biosensor technology which incorporates the latest advances in electrochemical, optoelectrical, piezoelectric, field effect transistors, and thermal transducer design. Even more promising approaches are now being explored resulting from advances made in the new frontiers of nanofabrication and molecular biology. One example of the latter is the exploitation of biological structures as the sensing elements of biosensors. This ‘hybrid’ approach represents a significant departure from ‘traditional’ chemical sensors which utilize strictly synthetic materials to detect biochemical events. The integration of advanced transducer design with complex, biologically active sensing elements holds great promise due to the superior detection capabilities offered by biological materials. Moreover, the newly emerging fields of molecular bioengineering and nanoengineering may ultimately provide the basis for the rational design of hybrid biosensors and other molecular-based devices as demonstrated by this feasibility study and other companion papers in this proceeding.

The line heat source method and the probe method for measurement of thermal conductivity are based on the same (or a very similar) theory. Both methods have been used to measure thermal conductivity of insulations, soils, biological materials, liquids, rocks, ceramics, and glass over a wide range of temperatures and other environmental conditions.

In the treatment of disease or injury it has been found that a variety of nonliving materials are of use. Commonplace examples include sutures and tooth fillings. A biomaterial is a synthetic material used to replace part of a living system or to function in intimate contact with living tissue. The Clemson University Advisory Board for Biomaterials has formally defined a biomaterial to be “a systemically and pharmacologically inert substance designed for implantation within or incorporation with living systems.” By contrast, a biological material is a material such as bone matrix or tooth enamel, produced by a biological system. Artificial materials that simply are in contact with the skin, such as hearing aids and wearable artificial limbs are not biomaterials since the skin acts as a barrier with the external world. The uses of biomaterials, as indicated in Table 1-1, include replacement of a body part that has lost function due to disease or trauma, to assist in healing, to improve function, and to correct abnormalities. The role of biomaterials has been influenced considerably by advances in many areas of medicine. For example, with the advent of antibiotics, infectious disease is less of a threat than in former times, so that degenerative disease assumes a greater importance. Moreover, advances in surgical technique have permitted materials to be used in ways that were not possible previously.

Processing of biological materials involves the application of a wide range of unit operations. These include procedures and equipment used in conventional bulk bioprocessing and more specialized or recently developed procedures especially suitable for the production of high value, high purity products from biotechnology. The more important general processing operations for mixing, heat transfer, size reduction and enlargement, and bulk separation will be discussed in this chapter.

Lasers could come to occupy a unique and very important position in the armament of medicine. They are the brightest known sources of light (man made or natural) on earth and as such can have extremely powerful effect on biological systems. Lasers are to other sources of light as music is to noise. The uniqueness of lasers derives from a number of special properties, viz., high intensity, coherence (which permits focusing to a spot size of one micrometer or less), collimation, extreme monochromaticity, and the ability to be delivered in very brief pulses. These collective properties can cause unique alterations of biological materials.

The processing of biological materials into useful products has been practised throughout the ages. Because of the dependence of mankind on food for survival, methods of preservation of agricultural produce to facilitate food storage have always been of prime concern. In addition, there has always been a need or desire to modify basic agricultural produce to separate out the digestible material and to improve food quality, especially with respect to flavour, taste and general palatability. Early processing methods reflected the availability and development of processing implements made from wood, stone, metal and other materials. Particularly in the last century, engineering aspects of bioprocessing have benefitted from developments in mechanization and the continual development of new equipment and synthetic processing materials. In addition, sophisticated automation and control methodologies arising from advances in electronics and computing are benefitting bioprocess engineering.

Since the high-water mark days of the 1960s when the combination of newly available isotope dilution spaces and the mathematics of compartmental analysis seemed on the verge of revolutionizing physiologic research (Bassingthwaighte, 1970), there has been a general decline in the applications of body composition methods to clinical medicine. In retrospect, concept outstripped competence, as the spaces that could be measured accurately, such as blood volume, turned out to be easier to cure (by transfusion) than to measure, and the mathematical expression of complex solutions for ferrokinetics and iodine kinetics through multiple compartments could rarely be turned to clinical benefit. The reasons were several, but important among them, a “respectable” standard error of measurement of ±5% was combined with a clinical uncertainty, at least as large, as to how “normal” could be defined. The terrain has now changed, in part because some new body compartments can be measured, in part because we have developed age-, sex-, and race- specific definitions of “normal”, but, in largest measure, because new precisions of measurement have been achieved, especially in the techniques of in-vivo neutron activation analysis. We shall consider some specific examples of their application. The benefits we envisage from high-precision in-vivo neutron activation (IVNA) derive largely iron understanding the interdependence of the body compartments, and, therefore, from the development of a series of models which interrelate the compartments.

The isolation of ecdysteroids from biological material is a skillful and lengthy process. Short cuts in that isolation, taking advantage of any special properties of ecdysteroids, would be a considerable help in their isolation, identification and quantitative analysis. One possible strategy would be to exploit the presence of vicinal diol systems found in many, if not most ecdysteroids, either at C-2 and C-3, or at C-20 and C-22, or both.

The viscous multicomponent mucin gel that coats the epithelial lining of the gastrointestinal tract is a heretofore neglected component of this organ system. The unique structural and functional characteristics of this biological material enable it to act as a protective physiological barrier to potentially deleterious agents. In addition, it may function to limit access to the intestinal surface and consequently limit absorption of nutrients.

There has been a great deal of discussion in the past few years on the mechanism of induction of chromosome aberrations by radiations and chemical agents, and also how similar alterations might arise “spontaneously.” This is an important issue, and yet it is perhaps of greater significance to determine how specific aberrations might be induced, i.e., are they formed by the same mechanism as aberrations in general or are they produced by a different process. Another way of stating this is, are specific aberrations, such as those observed in individuals with birth defects or those present in many tumors, a subset of total aberrations that are observed because of a particular phenotype that they, in part, elicit. This paper will address these various possibilities in the form of the development of a hypothesis, rather than by a review of the published literature.