For example, the first one I came across was the modification of internal lung tissues for better oxygen supply to the blood and greater resistance of their outer shell, the pulmonary pleura, to damage, in other cases, which would lead to impaired performance.
Like any organ in the body, the lungs perform not only gas exchange between man and nature, but also serve a number of secondary tasks, which Hyuga did not ignore - protection and cushioning of the heart, production of antimicrobial compounds in the mucous membrane that protect against respiratory infections, thermoregulation through evaporation of water, storage of a certain amount of blood, which can be used to restore the volume of the great circle of circulation at a great loss in case of injury by release into the circulatory system.
The latter is especially relevant for ninjas seeking to restore their fighting ability as soon as possible, and the ability to ignore, after modification, most of the volatile poisons that enter the bloodstream precisely through the lungs is something no one would refuse to get.
But the level of mastery of Shosen Jutsu (Mystic Hand Technique) is prohibitive, which not every second-degree iryonin can handle, given that the work is done literally at the cellular level, which I've only relatively recently begun to approach, focusing on keirakukei.
Actually, some of the techniques used by old man Hishi are available in the Nara clan library, but separately to improve the lung work in one direction, rather than a comprehensive method of approaching the modifications that was described in the notes.
Equally interesting was the part where the old iryonin gave his attention to the liver, which is one of the most important organs of any living creature, due to its function as a veritable chemical laboratory in the body.
It neutralizes various foreign substances, such as toxins, poisons, allergens, by transforming them into harmless or more easily removed from the body compounds; neutralizes or removes excess hormones and vitamins, as well as toxic intermediate and end products of metabolism; provides the energy needs of the body with glucose and converts into it various energy sources, such as amino acids, fatty acids, lactic acid, glycerol and similar substances; replenishes and stores rapidly mobilizable energy reserves g
It is possible to enumerate for a long time and not everything I personally knew from the mentioned by the old hrychom, but researches in the direction of improvement of liver functions were conducted by many in the hospital as the most suitable way of neutralization of poisons getting into the body, spread with the blood stream, documentation about what I studied in my time, but only the best even iryonins saved for themselves, sharing only the initial and the simplest developments.
I used the simplest methods of stimulation to develop immunity to poisons, but Hishi went much further in his work, if the records are to be believed - he achieved purification and renewal of blood composition by injecting into the blood a real battle cocktail of stimulants,
The Third Kazekage, who had used such poisons in the last war with his magnetism genkai, could attest to the fact that the normal liver was destroyed even in chakra users.
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