Brain freeze is the name used to describe the sensation you get when you consume something really cold, really fast. The scientific name for this temporary cold-stimulus headache is sphenopalatine ganglioneuralgia.

When something extremely cold touches the upper-palate (roof of the mouth), blood vessels in this region dilate to increase blood flow to counter the cold. The homeostatic triggers in your body perceive the cold as a threat to the brain, thinking the brain is in danger from the cold. As the warm blood rushes to your brain, this build-up of blood pressure causes the pain you feel. While brain freezes are not dangerous, they are slightly uncomfortable, so the best way to make it quickly go away is to rub or press your tongue against ...

Hemocyanins are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2). They are second only to hemoglobin in frequency of use as an oxygen transport molecule. Unlike the hemoglobin in red blood cells found in vertebrates, hemocyanins are not bound to blood cells but are instead suspended directly in the hemolymph. Oxygenation causes a color change between the colorless Cu(I) deoxygenated form and the blue Cu(II) oxygenated form. ...

Hippocrates (460–377 BC) postulated that the imbalance or excess of four fluids (called humors) within the body play a role in ones emotional and physical state. The chart below shows the four humors (row 1), the condition created by too much of each (row 2), and their respective emotions (row 3):


The Hippocratic theory of personality popularized the practice of bloodletting — opening a vein or applying leeches to "drain off" excessive amounts of the troublesome humor. In medieval Europe, it was common for barber-surgeons (whose professional practice relied on sharp instruments like knives and razors) to advertise their bloodletting services by posting a sign depicting a pale human arm traced with a crimson spiral of blood. (Remember that a ...

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A scanning electron microscope image of a single red blood cell on the tip of a needle.

The dragon’s blood tree (Dracaena draco) has a thick red resin that makes the plant appear to be bleeding when it is cut. These subtropical plants form huge umbrella-like canopies and can grow for hundreds of years, but they are currently listed as Vulnerable by the IUCN due to the trademark resin being used in traditional medicine, violin staining, and even for embalming the dead.

This is a white-blooded ice fish, or "crocodile fish" (Chaenocephalus aceratus). They lack both red blood cells and hemoglobin, and so have white blood. They have translucent bodies, and absorb oxygen directly from the water around them.