Regeneration According to Spallanzani

Total Page:16

File Type:pdf, Size:1020Kb

Regeneration According to Spallanzani DEVELOPMENTAL DYNAMICS 238:2357–2363, 2009 REVIEWS–A PEER REVIEWED FORUM Regeneration According to Spallanzani Panagiotis A. Tsonis* and Timothy P. Fox In this report, we elaborate on a letter that Spallanzani wrote to Bonnet reporting his findings on regeneration in worms, snails, tadpoles, and salamanders. The letter (original in French and translated in English; see Supplementary Material, which is available online) was written to discuss whether or not regeneration in these animals supports Bonnet’s theory on germs. The letter includes several drawings by Spallanzani, which were not published in the Prodromo, his book on Animal Reproduction. Spallanzani made important observations, which he described with considerable detail, but overall he was unable to confidently support Bonnet’s theory. This letter reflects the way of thinking in the 18th century that shaped the important scientific fields of regeneration and reproduction. Developmental Dynamics 238:2357–2363, 2009. © 2009 Wiley-Liss, Inc. Key words: Spallanzani; regeneration; animal reproduction Accepted 4 June 2009 INTRODUCTION of Creation. On the contrary, epigene- 1740 and on worm regeneration in sis allowed space for questioning the 1744 (Savioz, 1948; Dinsmore, 1991) Rooted in Aristotelian philosophy, the role of God. As expected when the first shocked the scientific world. Re´aumur belief that lower animals were gener- experiments in the 18th century re- and Bonnet were preformationists ated spontaneously from decay pre- vealed the regenerative power of ani- and, in fact, Re´aumur believed that vailed until the 17th century when mals, these two competing theories germs were contained within parts re- Redi in 1668 carried out well-con- trolled experiments that provided the were called upon to explain this new sponsible for regeneration. In his writ- property of animals. ings, Bonnet argued that Trembley’s first proof against it (Redi, 1668, th 1671). A similar view, epigenesis, de- The 18 century could very well be experiments with Hydra and his with veloped by Harvey, stated that new considered as the golden era in regen- worms supported the pre-existence of organisms appear from undifferenti- eration research. Many studies during germs and became a leading propo- ated matter. These ideas were sup- the previous century had led the way nent of the preformation theory. ported later in the 18th century by to understand how reproduction oc- Among these intellectual giants, Needhan and Buffon who believed curs and many theories and thoughts Lazzaro Spallanzani is also credited that organic molecules organized by were developed to explain how ani- as being one of the pioneers in regen- internal molds were responsible for mals (and humans) reproduce (Cobb, eration research. In 1768, Spallanzani animal generation (Benson, 1991). 2006). Naturally, scientists experi- published the Prodromo, his historical The rival position to epigenesis, which mented with regeneration in animals book on Animal Reproduction. At that prevailed at the end of the 17th cen- (which then was called actually repro- time, the word “reproduction” was tury, was preformation. According to duction). Pivotal discoveries by Re´au- used to denote “regeneration” as well. this, the organisms were preformed in mur on appendage regeneration in in- In his book, Spallanzani described the embryo. Preformation was also in sects in 1712 (Wheeler, 1926), by several types of regeneration with favor when it came to religious beliefs Tremblay on Hydra regeneration in mention of regeneration of the frog because it fit the notion that all gen- 1744 (Baker, 1952; Dawson, 1987), tail and salamander limbs. The ac- erations were established at the time and by Bonnet on parthenogenesis in counts were surprisingly quite short Additional Supporting Information may be found in the online version of this article. Department of Biology and Center for Tissue Regeneration and Engineering at Dayton, University of Dayton, Dayton, Ohio *Correspondence to: Panagiotis A. Tsonis, Department of Biology and Center for Tissue Regeneration and Engineering at Dayton, University of Dayton, Dayton, OH 45469-2320. E-mail: [email protected] DOI 10.1002/dvdy.22057 Published online 3 August 2009 in Wiley InterScience (www.interscience.wiley.com). © 2009 Wiley-Liss, Inc. 2358 TSONIS AND FOX Figs. 1–6. Anatomy and regeneration in worms. Fig. 1: The gross artery (red) attached to the intestines. Fig. 2: The artery branches into five vessels (red) as it reaches the head. Spallanzani describes the vessels as small bags composed of one or many constrictions. Fig. 3: The vein that runs from head to tail is winding. It is intersected by another vein, which is straightened. Fig. 4: The “boat” worm, a fresh water worm, whose tail is on the surface of the water (light blue), while the head is hidden in the mud (dark blue). Fig. 5: Regeneration in fresh water worm. A cone is produced. The reddish color at the base of the cone is the anus. Fig. 6: At the posterior part of the anus, a red line appears in the same direction as the artery of the animal (o). Spallanzani describes that at this stage he could not see circulation in the red line but later blood flows into the artery. with not much detail or any drawings sponded on September 14 and was nistic view of animal biology or how the that were common in publications of quite happy that Spallanzani shared issue of soul fits in a regenerating ani- that time. However, in a long letter to his views and that he was also work- mal). In addition, this letter also reflects Bonnet written on September 21, ing on earthworm regeneration. Bon- the clarity of thought that Spallanzani 1766, Spallanzani outlined in great net in a sense invited Spallanzani to possessed in order to explain his find- detail regeneration in many organ- pursue the work on earthworm regen- ings. We, therefore, strongly believe isms, including earthworm, snail, eration. An exchange of letters ensued that the contents of this letter should be frog, and salamander (Biagi, 1958; in which Spallanzani outlined a series of great historical value to scholars in Dinsmore, 1991). The letter, which of experiments that were inspired by developmental biology and regenera- reads as a research paper, is also dec- Bonnet’s influence. Bonnet mentioned tion research. Here we will highlight his orated with many drawings by Spal- that regeneration research should be major experiments and points. Also, we lanzani’s hand (original in French and able to resolve the germ concept, thus have reproduced the drawings and we translated in English can be found in inviting Spallanzani to elaborate on present them with added color as well. Supplementary Material). One of the this (Biagi, 1958; Dinsmore, 1991). The color is in accordance with the de- major reasons Spallanzani wrote this In his letter of September 21, Spal- scription that Spallanzani provides in letter was to discuss Bonnet’s theory lanzani casts doubts on the existence of on germs, according to which repro- germs for some types of regeneration his letter. Figures 1–17 have been set in duction and regeneration were medi- and obviously he does this with great the order in which they appear in the ated by germs that existed in the or- care not to offend Bonnet. Thus, this letter, but have been grouped according ganism. Spallanzani initiated letter bears enormous significance to the species. We will end this review correspondence with Bonnet on July about how scientists were thinking at by reflecting on how these ideas shaped th 18, 1765 by sending him copies of two that time and how they dealt with these scientific thought in the 18 century of his publications. On August 24, obstacles imposed by their social/reli- and how they relate to our thoughts in 1765, Spallanzani wrote again to Bon- gious status as well as by the prevailing the present day. Text in italics contains net critically commenting on Need- way of thinking of the time (for exam- comments by us related to Spallanza- ham and Buffon’s ideas. Bonnet re- ple, it questioned the Cartesian mecha- ni’s observations. REGENERATION ACCORDING TO SPALLANZANI 2359 REGENERATION IN ends of the head are dead but all the more or less equal parts. Almost all EARTHWORMS AND posterior parts containing the ovary the anterior parts regenerated (obvi- FRESHWATER WORMS and the small bags generated a head, ously these parts contained the repro- which in the end was equal to the orig- ductive system) while most of the pos- After a short salutation and com- inal one. terior parts (36/50) died. In the second ments on how some scientists view experiment, he cut the worm into three parts in a way that the anterior Bonnet’s research, Spallanzani sets Experiment 4 the stage by describing certain exper- part contained 3–6 rings and no re- iments he performed to learn about Divide longitudinally the body into productive system, and the middle the anatomy and physiology of the two parts from the head to two thirds part contained the reproductive sys- earthworm. Spallanzani provides of its length and then remove the pos- tem and the posterior part. At the end three drawings of the anatomy of ar- terior third (tail). Results: The two of the experiment, all the anterior teries and veins (Figs. 1–3). He then longitudinally divided parts and the parts were dead, the middle parts re- proceeds by outlining six different ex- tail part died. generated and many of the posterior periments to study regeneration in parts were alive but without signs of regeneration. Spallanzani also men- earthworm. Drawings outlining these Experiment 5 experiments and the results are tions that at the level of the tail, the shown in Supplementary Material. Divide the worm longitudinally into “boat” structure never failed to form, two parts from the tail to two thirds of and he also concludes that these Experiment 1 its length and then remove the ante- worms regenerate naturally because Transversal section of the earthworm rior part containing the head.
Recommended publications
  • Mechanisms of Urodele Limb Regeneration
    Received: 1 September 2017 Accepted: 4 October 2017 DOI: 10.1002/reg2.92 REVIEW Mechanisms of urodele limb regeneration David L. Stocum Department of Biology, Indiana University−Purdue University Indianapolis, Abstract 723 W. Michigan St, Indianapolis, IN 46202, USA This review explores the historical and current state of our knowledge about urodele limb regen- Correspondence eration. Topics discussed are (1) blastema formation by the proteolytic histolysis of limb tissues David L. Stocum, Department of Biology, Indiana to release resident stem cells and mononucleate cells that undergo dedifferentiation, cell cycle University−Purdue University Indianapolis, 723 W. Michigan St, Indianapolis, IN 46202, USA. entry and accumulation under the apical epidermal cap. (2) The origin, phenotypic memory, and Email: [email protected] positional memory of blastema cells. (3) The role played by macrophages in the early events of regeneration. (4) The role of neural and AEC factors and interaction between blastema cells in mitosis and distalization. (5) Models of pattern formation based on the results of axial reversal experiments, experiments on the regeneration of half and double half limbs, and experiments using retinoic acid to alter positional identity of blastema cells. (6) Possible mechanisms of distalization during normal and intercalary regeneration. (7) Is pattern formation is a self-organizing property of the blastema or dictated by chemical signals from adjacent tissues? (8) What is the future for regenerating a human limb? KEYWORDS limb, mechanisms, regeneration, review, urodele 1 INTRODUCTION encouraged the idea that mammals have retained a latent ances- tral genetic circuitry for appendage regeneration that might be Evidence from the fossil record indicates that urodeles (salaman- activated by appropriate interventions and applied to the goal of ders and newts) of the Permian period (the last period of the Pale- regenerating a human limb.
    [Show full text]
  • A Statistical Study of Regeneration in Two Species of Crustacea by W
    349 A STATISTICAL STUDY OF REGENERATION IN TWO SPECIES OF CRUSTACEA BY W. E. AGAR, Professor of Zoology, University of Melbourne. (Received 22nd April, 1930.) (With Three Text-figures.) CONTENTS. PAGE I. Introduction 349 II. Methods of culture 350 III. Growth and sex 351 IV. The material available . .351 V. Structure of the antenna 352 VI. The operation . • . 353 VII. General nature of the regeneration 353 VIII. Measuring and recording the amount of regeneration .... 355 IX. The influence of certain factors on regeneration ..... 357 (a) The segment through which amputation is performed . -357 (6) The level of amputation within the segment .... 357 W Age 358 (d) The simultaneous regeneration of the other antenna . 358 (e) The previous regeneration of the other antenna . -359 (/) Food 360 (g) General internal conditions of the animal 360 (h) General external conditions 361 X. The nature of the intrinsic factors controlling regeneration as disclosed by statistical analysis 362 XI. Discussion of results .......... 365 XII. Summary 367 I. INTRODUCTION. THIS study of regeneration in the two Cladoceran species, Simocephalus gibbosus and Daphnia carinata, grew out of a Lamarckian experiment on the possibility of improving (or otherwise altering) the power of regeneration in these animals by making them regenerate the antenna in many successive generations. Up to the present, these experiments have been completely negative in this respect, though they have furnished much data concerning the process of regeneration. The power of regeneration in a line of Simocephalus in which the antenna has been amputated a^»egenerated for seventy-four successive generations, and in a line of Daphnia for eighty generations, shows no difference from the power of regeneration of the JEB'VIliv 23 35° W.
    [Show full text]
  • La Logica Del Vivente in Maupertuis: Dall’Attrazione Newtoniana Al Determinismo Psicobiologico
    La logica del vivente in Maupertuis: dall’attrazione newtoniana al determinismo psicobiologico Federico Focher (Istituto di Genetica Molecolare “Luigi Luca Cavalli Sforza”, CNR, Pavia) Dopo aver rilanciato con successo la teoria epigenetica della generazione, reinterpretata alla luce dell’attrazione newtoniana e delle affinità chimiche (Vénus physique, 1745), Pierre-Louis Moreau de Maupertuis (1698-1759) approfondì le proprie indagini teoretiche nel campo della genesi degli organismi e delle specie nel Système de la Nature (1754). In quest’opera, al fine di conciliare il postulato di oggettività della scienza - che respinge il ricorso alle cause finali - con le evidenti proprietà teleonomiche degli esseri viventi, e riconoscendo nel contempo inadeguati a tale scopo i pur originali principii meccanicistici avanzati nella Vénus physique, Maupertuis propose un’ardita teoria panpsichista del vivente, di ispirazione spinoziana. Postulando quindi la materia viva, dotata di istinto e di sentimento, Maupertuis immaginò che una qualche forma di intelligenza o di memoria psichica, associata alla materia, dirigesse lo sviluppo dei viventi. Alla luce delle recenti scoperte della biologia, l’originale determinismo psicobiologico avanzato da Maupertuis nel Système de la Nature appare una geniale intuizione della logica dei processi genetici ed evolutivi. Keywords: Maupertuis, teleonomia, scienze della vita, storia della biologia, informazione genetica, panpsichismo, Buffon. Introduzione Mezzo secolo dopo la scoperta della legge della gravitazione universale
    [Show full text]
  • The Molecular Basis of Amphibian Limb Regeneration: Integrating the Old with the New David M
    seminars in CELL & DEVELOPMENTAL BIOLOGY, Vol. 13, 2002: pp. 345–352 doi:10.1016/S1084–9521(02)00090-3, available online at http://www.idealibrary.com on The molecular basis of amphibian limb regeneration: integrating the old with the new David M. Gardiner∗, Tetsuya Endo and Susan V. Bryant Is regeneration close to revealing its secrets? Rapid advances classical studies to guide the identification of the in technology and genomic information, coupled with several functions of this large set of genes. useful models to dissect regeneration, suggest that we soon The challenge of understanding the mechanisms may be in a position to encourage regeneration and enhanced controlling the biology of complex systems is hardly repair processes in humans. unique to regeneration biology. In recent years, techniques have become available to identify all the Key words: limb / regeneration / pattern formation / molecular components of a system, and to study the urodele / fibroblast / dedifferentiation / stem cells interactions between those components. Key to the success of such an approach is the ability to identify © 2002 Elsevier Science Ltd. All rights reserved. the molecules, while at the same time having an un- derstanding of the cell and tissue level properties of the system. The goal of this reviewis to discuss key insights from the classical literature as well as more recent molecular findings. We focus on three criti- Introduction cally important cell types: fibroblasts, epidermis and nerves. Each of these is necessary, and together they The study of amphibian limb regeneration has a rich are sufficient for the regeneration of a limb. Although experimental history.
    [Show full text]
  • The Spontaneous Generation Controversy (340 BCE–1870 CE)
    270 4. Abstraction and Unification ∗ ∗ ∗ “O`uen ˆetes-vous? Que faites-vous? Il faut travailler” (on his death-bed, to his devoted pupils, watching over him). The Spontaneous Generation Controversy (340 BCE–1870 CE) “Omne vivium ex Vivo.” (Latin proverb) Although the theory of spontaneous generation (abiogenesis) can be traced back at least to the Ionian school (600 B.C.), it was Aristotle (384-322 B.C.) who presented the most complete arguments for and the clearest statement of this theory. In his “On the Origin of Animals”, Aristotle states not only that animals originate from other similar animals, but also that living things do arise and always have arisen from lifeless matter. Aristotle’s theory of sponta- neous generation was adopted by the Romans and Neo-Platonic philosophers and, through them, by the early fathers of the Christian Church. With only minor modifications, these philosophers’ ideas on the origin of life, supported by the full force of Christian dogma, dominated the mind of mankind for more that 2000 years. According to this theory, a great variety of organisms could arise from lifeless matter. For example, worms, fireflies, and other insects arose from morning dew or from decaying slime and manure, and earthworms originated from soil, rainwater, and humus. Even higher forms of life could originate spontaneously according to Aristotle. Eels and other kinds of fish came from the wet ooze, sand, slime, and rotting seaweed; frogs and salamanders came from slime. 1846 CE 271 Rather than examining the claims of spontaneous generation more closely, Aristotle’s followers concerned themselves with the production of even more remarkable recipes.
    [Show full text]
  • Narrative and Natural History in the Eighteenth Century
    UCLA UCLA Previously Published Works Title Narrative and natural history in the eighteenth century. Permalink https://escholarship.org/uc/item/9x51z6qw Journal Studies in history and philosophy of science, 62 ISSN 0039-3681 Author Terrall, Mary Publication Date 2017-04-07 DOI 10.1016/j.shpsa.2017.03.009 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Studies in History and Philosophy of Science xxx (2017) 1e14 Contents lists available at ScienceDirect Studies in History and Philosophy of Science journal homepage: www.elsevier.com/locate/shpsa Narrative and natural history in the eighteenth century Mary Terrall Department of History, Box 951473, UCLA, Los Angeles, CA 90095-1473, USA article info abstract Article history: In the eighteenth century, natural histories of animals incorporated narratives about animal behaviour Available online xxx and narratives of discovery and experimentation. Naturalists used first-person accounts to link the stories of their scientific investigations to the stories of the animal lives they were studying. Under- Keywords: standing nature depended on narratives that shifted back and forth in any given text between animal and Narrative human, and between individual cases and generalizations about species. This paper explores the uses of Natural history narrative through examples from the work of René-Antoine Ferchault de Réaumur and Abraham René-Antoine de Réaumur Trembley. In all cases, narrative took the genre of natural history well beyond straightforward description Abraham Trembley fi Insects and classi cation. Prose accounts of insect actions and mechanisms worked in tandem with visual Metamorphosis narratives embedded in the accompanying illustrations, where artists developed strategies for repre- senting sequences of minute changes over time.
    [Show full text]
  • New Yorkers Had Been Anticipating His Visit for Months. at Columbia
    INTRODUCTION ew Yorkers had been anticipating his visit for months. At Columbia University, where French intellectual Henri Bergson (1859–1941) Nwas to give twelve lectures in February 1913, expectations were es- pecially high. When first approached by officials at Columbia, he had asked for a small seminar room where he could directly interact with students and faculty—something that fit both his personality and his speaking style. But Columbia sensed a potential spectacle. They instead put him in the three- hundred-plus-seat lecture theater in Havemeyer Hall. That much attention, Bergson insisted, would make him too nervous to speak in English without notes. Columbia persisted. So, because rhetorical presentation was as impor- tant to him as the words themselves, Bergson delivered his first American lec- ture entirely in French.1 Among the standing-room-only throng of professors and editors were New York journalists and “well-dressed” and “overdressed” women, all fumbling to make sense of Bergson’s “Spiritualité et Liberté” that slushy evening. Between their otherwise dry lines of copy, the reporters’ in- credulity was nearly audible as they recorded how hundreds of New Yorkers strained to hear this “frail, thin, small sized man with sunken cheeks” practi- cally whisper an entire lecture on metaphysics in French.2 That was only a prelude. Bergson’s “Free Will versus Determinism” lec- ture on Tuesday, February 4th—once again delivered in his barely audible French—caused the academic equivalent of a riot. Two thousand people attempted to cram themselves into Havemeyer. Hundreds of hopeful New Yorkers were denied access; long queues of the disappointed snaked around the building and lingered in the slush.
    [Show full text]
  • On the Trail of Digestion
    Middle School Science Eating to Live and Living to Eat Movement of Energy Through Living and Non-living Systems; Student Resource Matter, Its Structure and Changes; From Atoms to the Universe Name On the Trail of Digestion Read the following section on the history of medical science and answer the questions: January 17, 2002 SCoPE SC070104 Page 1 of 6 Middle School Science Eating to Live and Living to Eat Movement of Energy Through Living and Non-living Systems; Student Resource Matter, Its Structure and Changes; From Atoms to the Universe Spallanzani Lazzaro Spallanzani lived in the second half of the 18th Century. You may remember Spallanzani’s experiments on spontaneous generation. His work on digestion is also famous. In Spallanzani’s time, people knew that the stomach was a strong muscle that could grind and mash food. Investigations of bodies told scientists that. But Spallanzani believed that the stomach also held a chemical process. He began his studies using his own falcons. He would feed the falcons small pieces of meat attached firmly to a string, and when the meat had been in the birds stomachs for some time, he would remove it. (You might remember that birds regurgitate quite easily, and some birds feed their babies this way.) Spallanzani believed that digestion was a chemical process. Another noted scientist, Rene Reaumur disagreed. He wrote: "the gastric juice has no more effect out of the living body in dissolving or digesting the food than water, mucilage, milk, or any other bland fluid." Reaumur claimed to have done experiments to see if digestion could take place outside the body as well as in it.
    [Show full text]
  • The Mémoires of Abraham Trembley. III. His Discoveries on Hydra and His Approaches to Biology
    The mémoires of Abraham Trembley. III. His discoveries on hydra and his approaches to biology Autor(en): Lenhoff, Howard M. / Lenhoff, Sylvia G. Objekttyp: Article Zeitschrift: Archives des sciences et compte rendu des séances de la Société Band (Jahr): 38 (1985) Heft 3 PDF erstellt am: 29.09.2021 Persistenter Link: http://doi.org/10.5169/seals-740481 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. Das Veröffentlichen von Bildern in Print- und Online-Publikationen ist nur mit vorheriger Genehmigung der Rechteinhaber erlaubt. Die systematische Speicherung von Teilen des elektronischen Angebots auf anderen Servern bedarf ebenfalls des schriftlichen Einverständnisses der Rechteinhaber. Haftungsausschluss Alle Angaben erfolgen ohne Gewähr für Vollständigkeit oder Richtigkeit. Es wird keine Haftung übernommen für Schäden durch die Verwendung von Informationen aus diesem Online-Angebot oder durch das Fehlen von Informationen. Dies gilt auch für Inhalte Dritter, die über dieses Angebot zugänglich sind. Ein Dienst der ETH-Bibliothek ETH Zürich, Rämistrasse 101, 8092 Zürich, Schweiz, www.library.ethz.ch http://www.e-periodica.ch Arch. Sc. Genève Vol. 38 Fasc. 3 pp. 293-304 1985 THE MÉMOIRES OF ABRAHAM TREMBLEY: III. HIS DISCOVERIES ON HYDRA AND HIS APPROACHES TO BIOLOGY BY Howard M. LENHOFF1 and Sylvia G.
    [Show full text]
  • Key Answers) 1
    II PUC BIOLOGY ASSIGNMENT – 11 (KEY ANSWERS) 1. With a schematic representation, explain the life cycle of HIV. (5) The HIV (retro virus) gains entry into the body through sexual contact with an infected person. The virus then enters macrophages. In macrophages RNA genome of the virus replicates to form viral DNA with the help of reverse transcriptase enzyme. The viral DNA is incorporated into the host DNA and direct infected host cells (macrophages to produce viral particle. Therefore macrophages act as HIV factory. Simultaneously HIVB enters into T-lymphocytes (TH – Helper T-cells) where it replicates and produces progeny viruses. The progeny viruses released into the blood, attack the other helper T-lymphocytes. This is repeated leading to progressive decrease in the number of helper T – lymphocytes in the body. Due to decrease in the number of T – lymphocytes, the person suffers from infections such as Mycobacterium, viruses, fungi and even parasites like Toxoplasma. The person becomes immune deficient. This lead to his death. 2. The cells of malignant tumors are considered as dangerous. – Give reason. (1) Malignant tumors grow very rapidly, damage surrounding normal tissues and spread to other parts through blood stream where they get lodged and transform the normal cells into cancer cells. ASC INDEPENDENT P. U. COLLEGE Page 1 of 6 3. Explain the salient features of double helix model of DNA. (5) WATSON AND CRICK MODEL OF DNA (Double helix model) * Rosalind Franklin is best known for her work on the X-ray diffraction images (1952) of DNA, which led to the discovery of the DNA double helix model (1953) for which Francis Crick, James Watson, and Maurice Wilkins shared the Nobel Prize in Physiology or Medicine in 1962.
    [Show full text]
  • (DRIP) Glossary of Terms
    DRIP GLOSSARY Advance Regeneration - Seedling or saplings that are present in the understory prior to removal of any overstory trees. Age Class - A group of trees in a stand that are at or nearly the same age. Artificial Regeneration – Creation of a new age class by direct seeding, or by planting seedlings or cuttings, or by equipment scarification. Basal Area - Total area of cross section of tree stems measured at breast height (4 feet above the ground), usually expressed in square feet per acre. Biological Diversity - The distribution and abundance of different plant and animal communities. The number and equitability of communities, with landscapes possessing more and equitably distributed communities having the highest diversity. Clearcut - An even-age method of regenerating a stand through the removal, in a single cut, of all trees larger than seedling. The new age class develops in a fully-exposed microclimate. In some situations small numbers of trees may be left within the clear-cut opening for some special purpose. Composition, Stand - The proportion of each tree species in a stand expressed as a percentage of either the total number, basal area, or volume of all tree species in the stand. Community – An assemblage of two or more populations living together in the same geographical area at the same time. Conditional migrator – Deer that move shorter distances and/or migrate infrequently compared to obligate migrators. This occurs primarily in the southern Upper Peninsula and northern Lower Peninsula where winter is typically mild and severe winters occur periodically or 2 out of 10 years. Conditional Summer Range – Range occupied by conditional migratory deer during the snow free seasons of spring, summer and fall.
    [Show full text]
  • History of Microbiology: Spontaneous Generation Theory
    HISTORY OF MICROBIOLOGY: SPONTANEOUS GENERATION THEORY Microbiology often has been defined as the study of organisms and agents too small to be seen clearly by the unaided eye—that is, the study of microorganisms. Because objects less than about one millimeter in diameter cannot be seen clearly and must be examined with a microscope, microbiology is concerned primarily with organisms and agents this small and smaller. Microbial World Microorganisms are everywhere. Almost every natural surface is colonized by microbes (including our skin). Some microorganisms can live quite happily in boiling hot springs, whereas others form complex microbial communities in frozen sea ice. Most microorganisms are harmless to humans. You swallow millions of microbes every day with no ill effects. In fact, we are dependent on microbes to help us digest our food and to protect our bodies from pathogens. Microbes also keep the biosphere running by carrying out essential functions such as decomposition of dead animals and plants. Microbes are the dominant form of life on planet Earth. More than half the biomass on Earth consists of microorganisms, whereas animals constitute only 15% of the mass of living organisms on Earth. This Microbiology course deals with • How and where they live • Their structure • How they derive food and energy • Functions of soil micro flora • Role in nutrient transformation • Relation with plant • Importance in Industries The microorganisms can be divided into two distinct groups based on the nucleus structure: Prokaryotes – The organism lacking true nucleus (membrane enclosed chromosome and nucleolus) and other organelles like mitochondria, golgi body, entoplasmic reticulum etc. are referred as Prokaryotes.
    [Show full text]