invisible | Science and life

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Duke University staff describe in Science, probably one of the most unusual ways of hiding that can be found in the animal kingdom. We are talking about the glass frogs, which are called that, as you can guess, because of their translucent body. But if transparent skin is still imaginable, what can be done about other organs? How would it be, for example, with blood containing red erythrocytes floating in water, which supply all tissues with oxygen?

It all started when researchers wanted to find out how these frogs sleep. It turned out that during sleep they become even more transparent, as if all the blood had left their vessels somewhere. Where exactly it goes, she could understand with the help of photoacoustic images – a special method commonly used in engineering. In photoacoustic imaging, light pulses cause various molecules to vibrate, while emitting small portions of energy, so you can understand where and in what conditions they are. Such a trick could be performed on living sleeping frogs without disturbing them – which was especially important because the awake frogs quickly turned red with blood.

A sleeping glass frog (left) drives all the red blood cells into the liver and becomes even more transparent than when awake (right). (Photo: Jesse Delia/American Museum of Natural History)

All the red blood cells, as it turned out, in the sleeping glass frogs go to the liver, in special pockets inside it. Thanks to this, the frog becomes two to three times more transparent than usual; therefore, it is even more difficult to notice, which is very handy – while you are sleeping, you are easy to eat. A frog’s liver can be partially compared to an invisibility cloak, however, frogs still do not become absolutely invisible: the muscles become transparent, but some internal organs, including the liver, can still be distinguished in frogs.

At the same time, the heart continues to beat, but through the vessels it moves a more or less colorless liquid – blood without red blood cells. When the frog wakes up, the red blood cells leave the liver and the blood turns red. As for breathing, as we know, frogs breathe not only with their lungs, but with their entire skin. Probably, while resting, glass frogs have enough oxygen passing through the skin. By the way, there is at least one frog in the world without lungs at all – this is the Kalimantan barburula, which manages its entire life only with skin respiration.

Source: Autonomous non-commercial organization “Редакция журнала «Наука и жизнь»” from

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