a system and a method of the interaction and preservation of two or more reagents used in a chemical reaction is described , in which the reagents are put in contact one with another only when a buffer carrying a sample to be treated with said reagents breaks a partition barrier placed between two containers belonging to a device comprising a first upper container and a second lower container of a test tube , the bottom wall of the first container forming said partition barrier able to be perforated by the buffer carrying the sample to be treated .