全民知識王

Stomach acid is highly corrosive, capable of dissolving metal. However, the cells lining the stomach renew the mucosal layer completely every 3 to 4 days, protecting themselves from being digested by the acid.

Dolphins are aquatic mammals, and their nursing method has evolved a unique mechanism adapted to the underwater environment. Streamlined Body and Hidden Nipples To maintain a streamlined body that reduces drag while swimming in water, the nipples of female dolphins are normally hidden in **Mammary Slits** on the sides of their abdomen. The nipples only protrude slightly during nursing. Underwater Nursing Process Active Milk Ejection: Calves do not have flexible lips (they cannot suckle strongly like terrestrial mammals), so mother dolphins directly eject milk into the calf's mouth by contracting the muscles around their mammary glands. Tongue Forms a Seal: The calf curls its tongue into a tube to envelop the mother dolphin's nipple, and uses the serrated papillae on the edges of its tongue to create a tight seal, preventing seawater from mixing in or milk from dispersing into the water. Short and Frequent Feedings: Since calves need to surface frequently to breathe, each nursing session is usually very brief (ranging from a few seconds to tens of seconds), but is repeated dozens of times a day. High-Fat Milk Dolphin milk has a very high fat content (about 30% to 50%) and a thick, creamy, or milkshake-like consistency. The high-calorie milk allows calves to quickly build up a layer of blubber (cetacean fat) in a short period, providing not only warmth but also sufficient energy for swimming.

Dolphins primarily engage in **face-to-face (belly-to-belly)** mating, but may also adopt side-facing or rear-entry positions in certain situations. Genital Position: A dolphin's genital slit is located on its underside. To align their reproductive organs properly, two dolphins typically need to position themselves belly-to-belly, facing each other. Positional Variations: During mating, a common posture involves the male dolphin swimming below the female, flipping his belly upwards to face her, or both dolphins may engage side-by-side (crossed or parallel) to complete the act. Brief Duration: Maintaining specific positions in water requires overcoming resistance and buoyancy, so the actual copulation time for dolphins is very brief, usually only 10 to 20 seconds, though they will frequently repeat the act multiple times within that short period. Among mammals, besides humans and primates, dolphins are one of the few marine creatures that frequently engage in 'face-to-face/belly-to-belly' mating.

Dolphins can mate year-round without strict seasonal limitations. However, female dolphins have an ovulation period (estrus), meaning they cannot conceive throughout the entire year. Dolphin mating behavior can be broken down into the following characteristics: Mating is not limited to the breeding season (non-reproductive mating): Most wild animals only mate during the female's estrus period for the purpose of reproduction. But dolphins, similar to humans, engage in mating behavior 365 days a year. For them, mating is not just about producing offspring, but also for social bonding, consolidating group hierarchy, relieving stress, or simply seeking pleasure. Female dolphins are seasonally polyestrous (in heat): Although mating occurs at any time, the period when female dolphins can conceive is limited. Female dolphins are seasonally polyestrous animals (ovulating mainly between spring and autumn), and pregnancy can only occur if they mate with a male dolphin during their ovulation period. Rich sexual social behavior: The world of dolphins includes various social behaviors, such as same-sex behavior (e.g., long-term partnerships between male dolphins), daily physical contact between opposite sexes, and even using objects in their surroundings for self-stimulation. Therefore, the statement 'dolphins have no mating season' primarily refers to their ability to engage in mating activities at any time (mating does not equal entering estrus). However, when discussing the possibility of pregnancy, female dolphins still have a specific physiological ovulation cycle.

Yesterday, we introduced 'Wolf Girl' Dina, who was said to have lived with wolves. Today, let's meet another historically famous wild child – Victor of Aveyron. Around 1800, a boy estimated to be about 12 years old was found in the forests of southern France. No one knew his real name, who his parents were, or how long he had lived alone in the wild. Unlike Dina— Victor's story doesn't involve wolves 🐺❌ He had been long separated from human society when discovered, making him more accurately a 'wild child'. Later, French physician Itard took charge of him, named him Victor, and spent about 5 years trying to teach him language and various social living skills. Victor did make progress, understanding some language and learning some life skills, but he never developed normal spoken language abilities. Although Itard's initial expectations weren't fully met, this educational attempt from over 200 years ago became an important case in the history of special education development. As for why Victor lived alone in the forest, and what happened in his childhood— No one knows to this day. 🌲 So— A wolf girl can be a wild child, but a wild child doesn't necessarily have wolves! 😆

Research from Loughborough University and the University of Leicester in the UK found that soaking in hot water at 40 degrees Celsius for 1 hour can burn 126 calories, equivalent to walking for 25 to 30 minutes. For lowering blood sugar levels, the peak blood sugar level during a hot bath was 10% lower than when cycling. Researchers believe this is because bathing stimulates the body to synthesize more heat shock proteins, which help lower blood sugar.

A wolf boy refers to a human child who was raised by wolves or other wild animals from a young age, a type of 'Feral child'. In 1867, a boy estimated to be around 6 years old was discovered in northern India. According to records from the time, the boy was found living with wolves near a cave and was later taken to the Sikandra orphanage, where he was named Dina Sanichar. When he first entered human society, his behavior was very different from that of a typical child: he moved on all fours, sniffed food before eating, preferred raw meat, and was uncomfortable wearing clothes. As time passed, Dina gradually learned to wear clothes, eat cooked food, use cups and plates, and walk upright. However, despite living in human society for over 20 years, he never truly learned to speak. Yet, he did successfully learn one very human skill – smoking.🚬 Wearing clothes✔️ Using a cup✔️ Speaking human language❌ Smoking✔️ Did he misallocate his skill points somewhere?🤣 Dina died in 1895 and remains one of the most famous 'wolf boys' in history. Interestingly, though, while we can confirm Dina's existence, we cannot prove he was actually 'raised by wolves'. What truly happened in his childhood remains a mystery to this day.

Polar bear fur is indeed transparent and colorless. They appear white due to the physics of light refraction, and the skin underneath their fur is actually black. How Fur Appears White and Skin Absorbs Heat Hollow Structure: Polar bear hairs (guard hairs) contain no pigment and have a transparent, hollow shaft. Light Refraction and Scattering: When sunlight hits these hollow, transparent hairs, light repeatedly reflects and scatters between the hair's interior and the air pockets. This process reflects all wavelengths of light, which our eyes perceive as white, providing excellent camouflage in snowy environments. Black Skin for Efficient Heat Absorption: The skin beneath the fur is black, maximizing the absorption of solar heat conducted through the transparent hairs. Combined with up to 10 cm of subcutaneous fat and the insulating air within the hollow fur layer, this helps them retain body heat in extreme cold. Sometimes, in zoos, if microscopic algae grow within the hollow structure of polar bear fur, the hairs might temporarily appear greenish or yellowish. No wonder the polar bears at the zoo look kinda dirty @@

Research from the University of Surrey in the UK found that during traffic congestion, many cars stop at traffic lights and emit a large amount of exhaust fumes, leading to severe air pollution in the area. If you open your car windows at this time, passengers will inhale 25% of the harmful particles generated throughout the entire drive. When vehicles stop at intersections, decelerate, shift gears, or start and accelerate when the light turns green, they burn a significant amount of gasoline. Furthermore, due to the close proximity of cars, the concentration of inhalable particulate matter in the air near intersections is 29 times higher than in areas with smooth traffic flow.

As a mature sanitary protection product of modern times, the condom has had unexpected forms throughout history. In ancient and medieval times, people used a bizarre array of materials to achieve contraception and disease prevention. Archaeological data shows that ancient Egyptians used specially treated animal skins or linen to create protective covers. In 16th-century Europe, with the syphilis pandemic, Italian physician Gasparo Tagliacozzi invented an early 'condom' made of linen combined with chemical agents, specifically to combat sexually transmitted diseases. In the 18th and 19th centuries, animal by-products became mainstream. Processed sheep intestines, lamb cecums, or fish bladders were widely used in European society at the time to create reusable condoms. Although these products were expensive, cumbersome to clean, and had limited elasticity, they were an indispensable defensive tool for the aristocracy of the era. It wasn't until the invention of vulcanized rubber technology in 1839 that latex and rubber condoms in the modern sense were born and gradually popularized, completely changing human public health and reproductive choices.