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        Physicians may want to dig a little deeper into their closets, or grab their white coats on the way out of the operating room, if they want patients to view them __16__ , according to the largest-ever study of patient preferences for doctors’ attire. In fact, what medical doctors wear may matter more than most doctors—or even patients—might think, say the researchers of this project.

        Based on their findings, they __17__ more hospitals, health systems and practice groups to look at their dress standards for physicians, or create them if they __18__ . Just over half of the 4,062 patients surveyed in the clinics and hospitals of ten major medical centers said that what physicians wear is important to them—and more than one-third said that what a doctor wears influences their satisfaction with their care.

        “Professional dress on Wall Street, law and nearly every other industry is relatively clear—and it typically mirrors what applicants __19__ to their job interview,” says Christopher Petrilli, M.D., lead author of the study and an assistant professor of hospital medicine at the University of Michigan Medical School, who worked in the finance industry before entering medicine.

         “In medicine, the dress code is quite __20__ , but as physicians we should make sure that our attire reflects a certain level of professionalism that is also mindful of patients’ preferences,” explains Petrilli.

       The pandemic has underlined the extent __21__ digital interaction is no substitute for the real thing. In some ways, I’m more in touch with people than ever thanks to the numerous WhatsApp groups that revived themselves into a constant source of company. But __22__ away in a couple of group chats while absent-mindedly watching the latest Netflix offering doesn’t come close to the wonderful feeling of hugging a friend, or of spending three hours giving someone you haven’t seen for ages your undivided attention over a meal, or of having a conversation based not just on words but physical cues. I doubt the pandemic will seed a long-term distaste for crowds； if anything, I suspect that, if all goes well with the vaccine __23__ , the coming summer will see a crop of riotous street parties and carnivals. 

        As a teacher, the thought that this could happen somewhere children should be safe is unthinkable. But the truth is, it is time we were honest about the increasing encroachment of policing in our schools. This incident did not occur in a __27__ . Teachers, once seen as educators and caregivers, are under pressure to become plain-clothes police officers teaching algebra. 

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        Palaces are known for their beauty and splendor, but they offer little protection against attacks. It is easy to defend a fortress, but fortresses are not designed with the comfort of a king or queen in mind. When it comes to structures that are both majestic and well-fortified, the classic European castle is the pinnacle of design. Across the ages castles changed, developed, and eventually fell out of use, but they still command the fascination of the English culture. 

       Castles were originally built in England by Norman invaders in 1066. As William the Conqueror advanced through England, he fortified key positions to secure the land he had taken. The castles he built allowed the Norman lords to retreat to safety when threatened by English rebellion. Castles also served as bases of operation for offensive attacks. Troops were summoned to, organized around, and deployed from castles. In this way castles served both offensive and defensive roles in military operations.

        Not limited to military purposes, castles also served as offices from which the lord would administer control over his fiefdom. The lord of the land would hold court in his castle. Those who were socially beneath the lord would come to report the affairs of the lands that they governed and pay tribute to the lord. They would address disputes, handle business, feast, and enjoy festivities. In this way castles served as important social centers in medieval England. Castles also served as symbols of power. Built on prominent sites overlooking the surrounding areas, castles constantly loomed in the background of many peasants’ lives and served as a daily reminder of the lord’s strength. 

       The first castles constructed in England were made from earth and timber. Those who constructed them took advantage of natural features, such as hills and rivers, to increase defenses. Since these castles were constructed from wood, they were highly susceptible to attacks by fire. Wooden castles were gradually replaced by stone, which greatly increased the strength of these fortifications； however, being made from stone did not make these castles entirely fireproof. Attackers could hurl flaming objects into the castle through the windows or ignite the wooden doors. This led to moving the windows and entrances off of the ground floor and up to the first floor to make them more difficult to access.

      As the nobility accumulated wealth, England became increasingly attractive to those who sought to plunder. Raids by Vikings and other marauders increased in regularity. In response to these attacks, castle defenses were updated and improved. Arrow-slits were added. These were small holes in the castle, large enough for an arrow to fit through, which allowed defenders to fire from nearly invulnerable positions. Towers were built from which defenders could provide flanking fire. These towers were connected to the castle by wooden bridges, so that if one tower fell, the rest of the castle was still easy to defend. Multiple rings of castle walls were constructed, so that even if attackers made it past one wall, they would be caught on a killing ground between inner and outer walls. Advances such as these greatly increased the defense of castles.

    The demise of castles can ultimately be attributed to gunpowder. Gunpowder was first introduced to Europe during the 14th century, but the first gunpowder weapons were unreliable, inaccurate, and weak by later standards. During the 15th century, artillery became powerful enough to break through stone walls. This greatly undermined the military role of castles. Castles were then replaced by artillery forts that had no role in civil administration and country houses that were indefensible. Though castles no longer serve their original purposes, remaining castles receive millions of visitors each year from those who wish to experience these majestic vestiges of a time long passed.

        Xenobots, named after the African clawed frog (Xenopus laevis), are synthetic lifeforms that are designed by computers to perform some desired functions and built by combining together different biological tissues. Whether xenobots are robots, organisms, or something else entirely remains a subject of debate among scientists. 

        The first xenobots were built by Douglas Blackiston according to blueprints generated by an AI program. Xenobots built to date have been less than one millimeter wide and composed of just two things: skin cells and heart muscle cells, both of which are derived from stem cells harvested from early frog embryos. The skin cells provide rigid support and the heart cells act as small motors, contracting and expanding in volume to propel the xenobot forward. The shape of a xenobot’s body and its distribution of skin and heart cells are automatically designed in simulation to perform a specific task, using a process of trial and error (an evolutionary algorithm). 

       Xenobots have been designed to walk, swim, push pellets, carry payloads, and work together in a swarm to aggregate debris scattered along the surface of their dish into neat piles. They can survive for weeks without food and heal themselves after lacerations. Xenobots can also self-replicate via “kinetic replication”—a process that is known to occur at the molecular level but has never been observed before at the scale of whole cells or organisms. They can gather loose stem cells in their environment and form them into new xenobots with the same capability.

       Currently, xenobots are primarily used as a scientific tool to understand how cells cooperate to build complex bodies during morphogenesis. However, the behavior and biocompatibility of current xenobots suggest several potential applications to which they may be put in the future. 

       Given that xenobots are composed solely of frog cells, they are biodegradable. And as swarms of xenobots tend to work together to push microscopic pellets in their dish into central piles, it has been speculated that future xenobots might be able do the same thing with microplastics in the ocean: find and aggregate tiny bits of plastic into a large ball of plastic that a traditional boat or drone can gather and bring to a recycling center. Unlike traditional technologies, xenobots do not add additional pollution as they work and degrade: they behave using energy from fat and protein naturally stored in their tissue, which lasts about a week, at which point they simply turn into dead skin cells. In future clinical applications, such as targeted drug delivery, xenobots could be made from a human patient’s own cells, which would bypass the immune response challenges of other kinds of micro-robotic delivery systems. Such xenobots could potentially be used to scrape plaque from arteries, and with additional cell types and bioengineering, locate and treat diseases.

       The earliest recorded reference to oral disease is from an ancient (5000 BC) Sumerian text that describes “tooth worms” as a cause of dental decay, and there is historical evidence that the Chinese used acupuncture around 2700 BC to treat pain associated with tooth decay. And in ancient Egypt, written between 1700 and 1500 BC, there were references to substances to ease pain and treat decay in teeth. Aesculapius, a Greek physician, who lived between 1300 and 1200 BC is credited by many with the concept of extracting diseased teeth. Throughout the Middle Age in Europe, dentistry was made available to the wealthy by physicians who would go to their homes. Dentistry for the poorer people took place in the market places, where self-taught vagabonds would extract teeth for a small fee. From the Middle Ages to the early 1700s, much dental work was provided by so called “barber surgeons.” Pierre Fauchard (1678-1761), a French surgeon, is credited with being the “father of modern dentistry.” Dental practitioners migrated to the American colonies in the 1700s and devoted themselves primarily to the removal of diseased teeth and insertion of artificial dentures. Until the mid-1800s, dentures continued to be individually constructed by skilled artisans. Gold, silver, and ivory were common components, causing them to be very expensive and available only to the very wealthy. In1851 a process to mould material against a model of the patient’s mouth and attach artificial porcelain teeth allowed the manufacture of less expensive dentures. Later, acrylic plastics replaced the use of rubber and porcelain in denture construction. 

       A major contribution came from Horace Wells in 1844 when he initiated the use of nitrous oxide (laughing gas), founding the concept of inhalation analgesia and anesthesia. The medical community later adopted inhalation anesthesia as a standard surgical practice. Greene Vardiman Black (1831-1915) was the leading reformer of American dentistry. He devised a foot engine that allowed the dentist to keep both hands free while powering the dental drill. He also developed modern techniques for filling teeth based upon biological principles and microscopic evaluation, and proposed that dental caries and periodical disease were infections initiated by bacteria—not confirmed scientifically, however, until the early 1960s.

       For more than two years, people everywhere have been in the grip of a pandemic—but not necessarily the same one. In the affluent world, a viral respiratory disease, Covid, suddenly became a leading cause of death. In much of the developing world, by contrast, the main engine of destruction wasn’t this new disease, but its second-order effects: measures people took in response to the coronavirus. Richer nations and poorer nations differ in their vulnerabilities. 

      Whenever I talk with members of my family in Ghana, Nigeria and Namibia, I’m reminded that a global event can also be a profoundly local one. Lives and livelihoods have been affected in these places very differently from the way they have in Europe or the US.

       That’s true in the economic and educational realms, but it’s true, too, in the realm of public health. And across all these realms, the stakes are often life or death. The three countries I mentioned have a median age between 18 and 22 years, and the severity of Covid discriminates sharply by age. A big way that Covid can kill is by hampering the management of other diseases, such as HIV, malaria and TB. In Africa alone, 26 million people are living with HIV and, in a typical year, several hundreds of thousands die of it, while malaria, which is especially deadly to infants and toddlers, claims almost 400,000 lives.

      Those are big numbers, and yet they used to be much bigger—a major healthcare effort brought them down. Amid the pandemic, though, people stopped visiting clinics, in part because it became harder to get to them, and healthcare workers had to curtail their own movements. According to a Global Fund survey of 32 countries in Africa and Asia, prenatal care visits dropped by two-thirds between April and September 2020； consultations for children under five dropped by three-quarters.        Public-health experts predict that, as an indirect consequence of the Covid pandemic, twice as many people around the world could be at risk of dying from malaria. There could be 400,000 extra deaths from TB in the next few years, and half a million extra deaths from HIV. Across much of the world, in short, the response to the coronavirus has ushered in a shadow pandemic. The coronavirus’s real death toll, then, has to be calculated not just in deaths from Covid, but also in deaths that would otherwise have been prevented, from malaria, TB, HIV, diabetes and more. 

      This shadow pandemic isn’t simply a story about disease—it’s about poverty, hunger, truncated education and stunted lives. A suggestive comparison can be made with the climate crisis. In the affluent world, some people think of climate breakdown as a matter of how long the air conditioning stays on, but for many in the developing world, it’s already a matter of floods, droughts and famine.