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Displaying 101 - 125 of 1046 items.

Beadle's One Gene-One Enzyme Hypothesis

Between 1934 and 1945, George Beadle developed a hypothesis that each gene within the chromosomes of organisms each produced one enzyme. Enzymes are types of proteins that can catalyze reactions inside cells, and the figure shows that each enzyme controls a stage in a series of biochemical reactions. The top box in this figure represents a normal process of enzyme production and biochemical reactions, and the bottom box shows how Beadle's experiments affected the normal biochemical process.

Format: Graphics

Subject: Theories, Processes

Embryos in Wax (2002), by Nick Hopwood

Embryos in Wax: Models from the Ziegler Studio is a history of embryo wax modeling written by science historian Nick Hopwood. Published by the Whipple Museum of the History of Science University of Cambridge and the Institute of the History of Medicine University of Bern, 2002, the book, like the wax models, helps exemplify the visual and material culture of science.

Format: Articles

Subject: Publications

Gamete Intra-Fallopian Transfer (GIFT)

Various techniques constitute assisted reproduction, one of which is gamete intra-fallopian transfer (GIFT). The first example of GIFT involved primates during the 1970s; however, the technology was unsuccessful until 1984 when an effective GIFT method was invented by Ricardo Asch at the University of Texas Health Sciences Center and the procedure resulted in the first human pregnancy. The GIFT technique was created in hopes of generating an artificial insemination process that mimicked the physiological sequences of normal conception.

Format: Articles

Subject: Technologies, Reproduction

Ernest Everett Just (1883-1941)

Ernest Everett Just was an early twentieth century American experimental embryologist involved in research at the Marine Biological Laboratory (MBL) at Woods Hole, Massachusetts, and the Stazione Zoologica in Naples, Italy. Just was known for simple but elegant experiments that supported the "fertilizing" theory of Frank R. Lillie and served as an antagonist to Jacques Loeb's work with artificial parthenogenesis.

Format: Articles

Subject: People

George Wells Beadle (1903-1989)

George Wells Beadle studied corn, fruit flies, and funguses in the US during the twentieth century. These studies helped Beadle earn the 1958 Nobel Prize in Physiology or Medicine. Beadle shared the prize with Edward Tatum for their discovery that genes help regulate chemical processes in and between cells. This finding, initially termed the one gene-one enzyme hypothesis, helped scientists develop new techniques to study genes and DNA as molecules, not just as units of heredity between generations of organisms.

Format: Articles

Subject: People

“Diethylstilbestrol in the Prevention and Treatment of Complications of Pregnancy” (1948), by Olive Watkins Smith

In 1948, Olive Watkins Smith published 'Diethylstilbestrol in the Prevention and Treatment of Complications of Pregnancy' in the American Journal of Obstetrics and Gynecology. In 632 women treated with diethylstilbestrol, Smith demonstrated that the drug stimulated the production of progesterone, a hormone that regulates the uterine condition during pregnancy.

Format: Articles

Subject: Publications

Roger Wolcott Sperry (1913–1994)

Roger Wolcott Sperry
studied the function of the nervous system in the US during the
twentieth century. He studied split-brain patterns in cats and
humans that result from separating the two hemispheres of the
brain by cutting the corpus callosum, the bridge between the two
hemispheres of the brain. He found that separating the corpus
callosum the two hemispheres of the brain could not communicate
and they performed functions as if the other hemisphere did not

Format: Articles

Subject: People

American Eugenics Society (1926-1972)

The American Eugenics Society (AES) was established in the US by
Madison Grant, Harry H. Laughlin, Henry Crampton, Irving Fisher, and
Henry F. Osborn in 1926 to promote eugenics education programs for
the US public. The AES described eugenics as the study of improving
the genetic composition of humans through controlled reproduction of
different races and classes of people. The AES aided smaller eugenic
efforts such as the Galton Society in New York, New York, and the

Format: Articles

Subject: Organizations

Paul Eugen Bleuler (1857–1939)

Paul Eugen Bleuler studied autism and schizophrenia, among other psychiatric disorders, throughout continental Europe in the early twentieth century. Bleuler worked as a psychiatrist caring for patients with psychiatric disorders at a variety of facilities in Europe. In 1908, Bleuler coined the term schizophrenia to describe a group of diseases that cause changes in thought processes and behavior in humans as well as difficulties relating to the world.

Format: Articles

Subject: People

Ernst Heinrich Philipp August Haeckel (1834-1919)

Ernst Heinrich Philipp August Haeckel was a prominent comparative anatomist and active lecturer in the late nineteenth and early twentieth centuries. He is most well known for his descriptions of phylogenetic trees, studies of radiolarians, and illustrations of vertebrate embryos to support his biogenetic law and Darwin's work with evolution. Haeckel aggressively argued that the development of an embryo repeats or recapitulates the progressive stages of lower life forms and that by studying embryonic development one could thus study the evolutionary history of life on earth.

Format: Articles

Subject: People

The Source-Sink Model

The source-sink model, first proposed by biologist Francis Crick in 1970, is a theoretical system for how morphogens distribute themselves across small fields of early embryonic cells. A morphogen is a substance that determines the fate and phenotype of a group of cells through a concentration gradient of itself across that group. Crick’s theory has been experimentally confirmed with several morphogens, most notably with the protein bicoid , the first discovered morphogen. The model provides a theoretical structure for the understanding of some features of early embryonic development.

Format: Articles

Subject: Theories

Nicolaas Hartsoeker (1656-1725)

Nicolaas Hartsoeker, a Dutch astronomer, optics manufacturer, and naturalist, was born 26 March 1656 in Gouda, Netherlands, and died 10 December 1725. His mother was Anna van der Mey and his father was Christiaan Hartsoeker, a prominent evangelical minister. His major contribution to embryology was his observations of human sperm cells, which he claimed to be the first to see under a microscope. His sketch of the homunculus, a tiny preformed human he believed to exist in the head of spermatazoa, is his lasting scientific legacy in the field of embryology.

Format: Articles

Subject: People

Dana Louise Raphael (1926–2016)

Dana Louise Raphael was an anthropologist and breastfeeding advocate in the US during the twentieth century. After she was unable to breastfeed her own infant, Raphael began to research why breastfeeding was more common in other cultures than in the US. As part of that research, Raphael cofounded the Human Lactation Center, where she studied the breastfeeding habits of mothers around the world. Through that research, she coordinated with formula manufacturers to educate women on the benefits of breastfeeding and formula supplementation to reduce infant mortality in developing nations.

Format: Articles

Subject: People

The Infant Incubator in Europe (1860-1890)

In the nineteenth century, obstetricians in Europe began to construct devices to incubate infants in increasingly controlled environments. The infant incubator is a medical device that maintains stable conditions and a germ free environment for premature infants born before the thirty-seventh week of pregnancy. Records show that physicians had used infant incubators since 1835. However, Jean-Louis-Paul Denuce, a physician who worked in Bordeaux, France, first published about incubator technology in 1857.

Format: Articles

Subject: Technologies, Reproduction

Spermism

Spermism was one of two models of preformationism, a theory of embryo generation prevalent in the late seventeenth through the end of the eighteenth century. Spermist preformationism was the belief that offspring develop from a tiny fully-formed fetus contained within the head of a sperm cell. This model developed slightly later than the opposing ovist model because sperm cells were not seen under the microscope until about 1677.

Format: Articles

Subject: Theories

Preformationism in the Enlightenment

Preformationism was a theory of embryological development used in the late seventeenth through the late eighteenth centuries. This theory held that the generation of offspring occurs as a result of an unfolding and growth of preformed parts. There were two competing models of preformationism: the ovism model, in which the location of these preformed parts prior to gestation was the maternal egg, and the spermism model, in which a preformed individual or homunculus was thought to exist in the head of each sperm.

Format: Articles

Subject: Theories

Charles Bonnet (1720-1793)

Charles Bonnet was a naturalist and philosopher in the mid eighteenth century. His most important contribution to embryology was the discovery of parthenogenesis in aphids, proving that asexual reproduction of offspring was possible. In his later life, he was an outspoken defender of the theory of generation now known as preformationism, which stated that offspring exist prior to conception preformed in the germ cell of one of their parents.

Format: Articles

Subject: People

Parasitic Twins

Parasitic twins, a specific type of conjoined twins, occurs when one twin ceases development during gestation and becomes vestigial to the fully formed dominant twin, called the autositic twin. The underdeveloped twin is called parasitic because it is only partially formed, is not functional, or is wholly dependent on the autositic twin.

Format: Articles

Subject: Disorders, Reproduction

Artificial Parthenogenesis and Fertilization (1913), by Jacques Loeb

Jacques Loeb is best known for his embryological work investigating parthenogenesis in invertebrates. Artificial Parthenogenesis and Fertilization is a revised and English-translated work from his earlier book, Die chemische Entwicklungserregung des tierischen Eies (1900). Artificial Parthenogenesis describes Loeb's many and varied methodical experiments to initiate egg development without fertilization by sperm. As is true with much of science, some of Loeb's experiments were successful and many were not.

Format: Articles

Subject: Publications

Maurice Ralph Hilleman (1919–2005)

Maurice Ralph Hilleman developed vaccines at the Merck Institute of Therapeutic Research in West Point, Pennsylvania, during the twentieth century. Over the course of his career at Merck, Hilleman created over forty vaccines, making him one of the most prolific developers of vaccine in the twentieth century. Of the fourteen vaccines commonly given to children in the US by 2015, Hilleman was responsible for eight of them. Hilleman's most widely used vaccine was his measles, mumps, and rubella (MMR) vaccine.

Format: Articles

Subject: People

Essay: Homology

Homology is a central concept of comparative and evolutionary biology, referring to the presence of the same bodily parts (e.g., morphological structures) in different species. The existence of homologies is explained by common ancestry, and according to modern definitions of homology, two structures in different species are homologous if they are derived from the same structure in the common ancestor.

Format: Essays and Theses

Subject: Processes

Santiago Felipe Ramon y Cajal (1852-1934)

Santiago Felipe Ramon y Cajal investigated brains in the nineteenth and twentieth centuries in Spain. He identified and individuated many components of the brain, including the neuron and the axon. He used chick embryos instead of adult animals, then customary in brain research, to study the development and physiology of the cerebellum, spinal cord, and retina. Ramon y Cajal received the Nobel Prize in Physiology and Medicine in 1906, along with Camillo Golgi, for his work on the structure of the nervous system.

Format: Articles

Subject: People

"The Developmental Capacity of Nuclei Taken from Intestinal Epithelium Cells of Feeding Tadpoles" (1962), by John B. Gurdon

In 1962 researcher John Bertrand Gurdon at the University of Oxford in Oxford, England, conducted a series of experiments on the developmental capacity of nuclei taken from intestinal epithelium cells of feeding tadpoles. In the experiments, Gurdon conducted nuclear transplantation, or cloning, of differentiated cells, or cells that have already specialized to become one cell type or another, in tadpoles. Gurdon's experiment showed that differentiated adult cells could be induced to an undifferentiated state, where they could once again become multiple cell types.

Format: Articles

Subject: Experiments

Ignacio Vives Ponseti (1914-2009)

Ignacio Vives Ponseti developed a noninvasive method for treating congenital club foot in the US during the late 1940s. Congenital club foot is a birth deformity in which one or both of an infant's feet are rotated inward beneath the ankle, making normal movement rigid and painful. Ponseti developed a treatment method, later called the Ponseti method, that consisted of a series of manipulations and castings of the club foot performed in the first few months of life.

Format: Articles

Subject: People

An Atlas of Fertilization and Karyokinesis of the Ovum (1895), by Edmund Beecher Wilson

Edmund Beecher Wilson in the US published An Atlas of Fertilization and Karyokinesis of the Ovum (hereafter called An Atlas) in 1895. The book presents photographs by photographer Edward Leaming that capture stages of fertilization, the fusion of sperm and egg and early development of sea urchin (Toxopneustes variegatus) ova, or egg cell. Prior to An Atlas, no one photographed of eggcell division in clear detail. Wilson obtained high quality images of egg cells by cutting the cells into thin sections and preserving them throughout different stages of development.

Format: Articles

Subject: Publications, Reproduction