The human intestine is a natural environment ecosystem of a complex of diversified and dynamic microorganisms, determined through a process of competition and natural selection during life. Those intestinal microorganisms called microbiota and are involved in a variety of mechanisms of the organism, they interact with the host and therefore are in contact with the organs of the various systems. However, they play a crucial role in maintaining host homeostasis, also influencing its behaviour. Thus, microorganisms perform a series of biological functions important for human well-being. The host provides the microorganisms with the environment and nutrients, simultaneously drawing many benefits such as their contribution to metabolic, trophic, immunological, and other functions. For these reasons it has been reported that its quantitative and qualitative composition can play a protective or harmful role on the host health. Therefore, a dysbiosis can lead to an association of unfavourable factors which lead to a dysregulation of the physiological processes of homeostasis. Thus, it has previously noted that the gut microbiota can participate in the pathogenesis of autoimmune diseases, chronic intestinal inflammation, diabetes mellitus, obesity and atherosclerosis, psychic disorders (e.g., neurological diseases, autism, etc. ) colorectal cancer, and more.

This study deals with the letter (dad). The effort concentrates in this study on all sides of that letter, direct and indirect. For example: accusing it with stuburn, individuality in the Arabic linguistically system, definition its way out, mention its ledges, description its creation, After that look out colored phonetics, free and halted to (dad), analyze it according to temporary linguistic enlture. The study showed that (dad) letter is stubborn but not impossible. And Arabic language does not itemize it. It us the most changeable letter in Arabic language, and so its changes increased and extended. The total changes and free varied coloring phonetics to that sound (dad), either justificated or not, it reached fourteen changes plus limited changes (philiulogical) assimilated in contrast, similarity, and incorporation. تتناول هذه الدراسة صوت (الضاد)، والسعي مركوز في هذه الدراسة على جلّ جوانب هذا الصوت، سواء الجوانب المباشرة أو غير المباشرة، نحو: اتهامه بالعصي، والتفرد في النظام اللغويّ العربيّ، وتحديد مخرجه، وذكر صفاته، وتوصيف آلية تكوينه، ثم رصد التلونات الصوتية الحرة والمقيدة للضاد، وتحليلها على اهتداء من الثقافة اللغوية اللسانية المعاصرة. وأظهرت الدراسة أنّ صوت الضاد صوت عسير وليس عصيا، وأنّه لم تتفرد العربية به فحسب، وهو من أكثر الأصوات العربية تبدلاً، فكثُرتْ إبدالاته واتسع التصرف به، فمجموع التبدلات والتلونات الصوتية الحرة (الفوناتيكية) لصوت الضاد، سواء كانت مبررة أو غير مبررة بلغت أربعة عشر تبدلاً، بالإضافة إلى التبدلات المقيدة (الفونولوجيّة) والمتمثلة بالمخالفة والمماثلة والإدغام.