He was the first European to describe in detail the process of making gun¬ powder, and he proposed flying machines and motorized ships and carriages. He therefore represents a historically precocious expression of the empirical spirit of experimental science, even though his actual prac¬ tice of it seems to have been exaggerated. His philosophical thought was essentially Aristotelian, though he was critical of the methods of theolo¬ gians such as Albertus AAagnus and Thomas Aquinas, arguing that a more accurate experimental knowledge of nature would be of great value in confirming the Christian faith. He also wrote on mathematics and logic. He was condemned to prison c. 1277 by his fellow Franciscans because of “suspected novelties” in his teaching.
bacteremia V.bak-te-'re-me-oN Presence of bacteria in the blood. Short¬ term bacteremia follows dental or surgical procedures, especially if local infection or very high-risk surgery releases bacteria from isolated sites. In some cases, prior antibiotic therapy can prevent this. It causes little problem to a healthy immune system but can be serious for those with prostheses (where infection can center) or high susceptibility to bacterial invasion. Extensive bacteremia can release toxins into the blood (septice¬ mia), leading to shock and vascular collapse. Antibiotic-resistant bacteria have increased the rate of severe bacteremia.
bacteria Group of microscopic, single-celled organisms that are prokaryotes. They may have spherical, rodlike, or spiral shapes. They inhabit virtually all environments, including soil, water, organic matter, and the bodies of multicellular animals. Different types are distinguished in part by the structure of their cell walls, which is determined by gram stain. Many bacteria swim by means of flagella (see flagellum). The DNA of most bacteria is found in a single circular chromosome and is distrib¬ uted throughout the cytoplasm rather than contained within a membrane- enclosed nucleus. Though some bacteria can cause food poisoning and infectious diseases in humans, most are harmless and many are benefi¬ cial. They are used in various industrial processes, especially in the food industry (e.g., the production of yogurt, cheeses, and pickles). Bacteria are divided into eubacteria and archaebacteria. See also budding bacteria,
COLIFORM BACTERIA, CYANOBACTERIA, DENITRIFYING BACTERIA, NITRIFYING BACTERIA, SHEATHED BACTERIA, SULFUR BACTERIA.
bacterial diseases Diseases caused by bacteria. The most common infectious diseases, they range from minor skin infections to bubonic plague and tuberculosis. Until the mid-20th century, bacterial pneumonia was probably the leading cause of death among the elderly. Improved sanitation, vaccines, and antibiotics have all decreased the mortality rates from bacterial infections, though antibiotic-resistant strains have caused a resurgence in some illnesses. Bacteria cause disease by secreting or excreting toxins (as in botulism), by producing toxins internally, which are released when the bacteria disintegrate (as in typhoid), or by inducing sen¬ sitivity to their antigenic properties (as in tuberculosis). Other serious bac¬ terial diseases include cholera, diphtheria, bacterial meningitis, and syphilis.
bacteriology Study of bacteria. Modern understanding of bacterial forms dates from Ferdinand Cohn’s classifications. Other researchers, such as Louis Pasteur, established the connection between bacteria and fermen¬ tation and disease. The modern methods of bacteriological technique began in the late 19th century with the use of stains and the development of methods of cultivating organisms on plates of nutrients. Important dis¬
coveries came when Pasteur succeeded in immunizing animals against two bacterial diseases, which led to the development of immunology. See also microbiology.
bacteriophage \bak-'tir-e-3-,faj\ or phage Any of a group of usu¬ ally complex viRUSes that infect bacteria. Discovered in the early 20th cen¬ tury, bacteriophages were used to treat human bacterial diseases such as bubonic plague and cholera but were not successful; they were abandoned with the advent of antibiotics in the 1940s. The rise of drug-resistant bac¬ teria in the 1990s focused renewed attention on the therapeutic potential of bacteriophages. Thousands of varieties exist, each of which may infect only one or a few types of bacteria. The core of a bacteriophage’s genetic material may be either DNA or RNA. On infecting a host cell, bacterioph¬ ages known as lytic or virulent phages release replicated viral particles by lysing (bursting) the host cell. Other types, known as lysogenic or temperate, integrate their nucleic acid into the host’s chromosome to be replicated during cell division. During this time they are not virulent. The viral genome may later become active, initiating production of viral par¬ ticles and destruction of the host cell. A.D. Hershey and Martha Chase used a bacteriophage in a famous 1952 experiment that supported the theory that DNA is the genetic material. Because bacteriophage genomes are small and because large quantities can be prepared in the laboratory, they are a favourite research tool of molecular biologists. Studies of phages have helped illuminate genetic recombination, nucleic acid repli¬ cation, and protein synthesis.
Bactria Ancient country, Central Asia. It was situated between the Hindu Kush and the Amu Darya in parts of modern Afghanistan, Uzbekistan, and Tajikistan. Its capital was the city of Bactra. From the 6th century bc it was controlled by the Achaemenian dynasty; conquered by Alexander the Great, the area was ruled after his death (323 bc) by the Seleucid dynasty and for a time (c. 250 bc) formed an independent kingdom. It was long important as a crossroads for overland trade and as a meeting place for various religious and artistic traditions. The area ultimately came under Muslim control in the 7th century ad.
Baden \‘bad- 3 n\ Former German state, southern Germany. The name (meaning “baths”) refers to the warm mineral springs, particularly in the town of Baden-Baden, valued since Roman times. Baden first became a political unit in 1112. Split up many times, the territory was finally reunited under Charles Frederick in 1771. A centre of 19th-century lib¬ eralism, it was active in the revolutions of 1848-50. It joined the German Empire in 1871 and became part of the Weimar Republic in 1919. After World War II, Baden was incorporated into West Germany as part of Baden-Wiirttemberg state.
Baden and Rastatt, Treaties of See Treaties of Rastatt and Baden
Baden-Powell Vba-d 3 n-'p6-3l\ (of Gilwell), Robert Stephen¬ son Smyth, 1st Baron (b. Feb. 22, 1857, London, Eng.—d. Jan. 8, 1941, Nyeri, Kenya) British army officer and founder of the Boy Scouts and Girl Guides (later Girl Scouts; see scouting). He was noted for his use of observation balloons in warfare in Africa (1884-85). In the South African War, he became a national hero in the Siege of Mafikeng. Hav¬ ing learned that his military textbook Aids to Scouting (1899) was being used to train boys in woodcraft, he wrote Scouting for Boys (1908) and that same year established the Boy Scout movement. In 1910, with his sister Agnes and his wife, Olave, he founded the Girl Guides.
badger Any of eight species of stout-bodied carnivores (family Mus- telidae) that possess an anal scent gland, powerful jaws, and large, heavy claws on their forefeet. Most species are brown, black, or gray, with markings on the face or body, and are found in South Asia. Badgers dig to find food and to construct burrows and escape routes. The American badger (Taxidea taxus ), the only New World species, lives in the open, dry country of western North America. Badgers feed mostly on small ani¬ mals, especially rodents. Species may be 9-12 in. (23-30 cm) high and 13-32 in. (33-81 cm) long, excluding the 2- to 10-in. (5- to 23-cm) tail, and may weigh 2^18 lbs (1-22 kg). Badgers can be savage fighters.