Straw for the preservation of a predetermined dose of liquid-based substance

A straw for the preservation of a predetermined dose of liquid-based substance, comprising a tube extending between a first end and a second end and comprising a liquid-tight, gas-permeable stopper, which stopper being disposed in the tube dose to its first end and extending between a first end turned towards the first end of the tube and a second end turned towards the second end of the tube, said stopper and said tube being configured so that after the liquid-based substance has come to meet the stopper by its second end, the stopper blocks the passage of the liquid-based substance and, by pushing on its first end, can be slid in the tube towards the second end of the tube, wherein said tube is of thermochromic material having a reversible change in hue at a predetermined temperature threshold, whereby the tube has a first visual appearance if its temperature is below said predetermined threshold and a second visual appearance different from the first visual appearance if its temperature is above said predetermined threshold, and wherein the tube is transparent or translucent when it has the first appearance and when it has the second appearance, the stopper being visible through the tube, said tube having a small wall thickness configured such that the temperature of the part of the tube that surrounds the liquid-based substance matches that of the liquid-based substance.