「趣聞」澳洲袋熊如何製造方形便便？ 20190922 How do wombats make cubed poo?

How do wombats make cubed poo?

Patricia J Yang (Georgia Inst of Tech), Miles Chan (Georgia Inst of Tech), Scott Carver (University of Tasmania, Australia), David L Hu (Georgia Inst of Tech)

This abstract is published in a scientific meeting: 71st Annual Meeting of the APS Division of Fluid Dynamics

Wombats are fossorial herbivorous Australian marsupials with the distinctive feature of producing cubic feces, which is unique in the animal kingdom. In the built world, cubic structures are created by extrusion or injection molding, but there are few examples of this feat in nature. We investigate how wombats produce cubic feces, through investigation of the structure and mechanics of two dissected alimentary systems of wombats--derived from veterinary euthanized individuals following motor vehicle collisions in Tasmania, Australia. In the final 8 percent of the intestine, feces changed from a liquid-like state into a solid state composed of separated cubes of length 2 cm. This shape change was due to the azimuthally varying elastic properties of the intestinal wall. By emptying the intestine and inflating it with a long balloon, we found that the local strain varies from 20 percent at the cube's corners to 75 percent at its edges. Thus, the intestine stretches preferentially at the walls to facilitate cube formation. This study addresses the long-standing mystery of cubic scat formation and provides insight into new manufacturing techniques for non-axisymmetric structures using soft tissues.

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澳洲袋熊如何製造方形的便便？

＊我試著在網路上找尋這篇研究的論文，但是並沒有發現全文的部分，也許現在在投稿中，又或許目前只有在會議上發表，不得而知。

摘要

袋熊是生長於澳洲的穴居有袋動物，袋熊有著非常特殊的特色-排放立方體形狀的糞便，這個現象在動物界中是非常獨特的。在製造業中，立方體的形狀是經由擠壓獲釋注射至鑄模中而製造出來的，但在大自然中，有少數的例子可以製造出立方體。我們利用研究兩隻在受到碰撞受傷後，經由獸醫施行安樂死並解剖的袋熊消化系統來了解，為何袋熊可以製造出方形的排泄物。在最後8%的腸道中，排泄物開始從液體狀的型態進入固體狀態，並且由大約兩公分大小的立方體顆粒所組成。這個形狀上的變化是由於腸道壁的不同部位有不同的彈性所造成的。

在清空腸道後，我們將長型的氣球置於腸道中並且充氣，我們發現在形成立方體的角落部位，有約20%的彈性張力，而在立方體邊的部分約有75%的彈性張力。因此腸道在部分區域張力的差異，促成立方體的行程。這個研究在解開了如何形成方形排遺這個一直存在的疑惑，並且對於可能利用軟性材料來製造軸對稱物質的新製程，提供了一線曙光。

左圖：澳洲袋熊

圖片來源：https://img1.etsystatic.com/004/0/6078251/il_570xN.384446343_a47d.jpg

右圖：袋熊的糞便

圖片來源：https://www.sciencenews.org/article/how-wombats-poop-cubes