"An organism in perfect represents health. This fine balance, even in the presence of adverse environment factors, is a resultant of different process that are going on within and which maintain the optimum conditions. In the higher forms of life the neuro- endocrine system represents the homeostatic control which regulates the various process of anabolism and catabolism. This fine regulations is feasible only as long as a predetermined response follows a given stimulus. This is possible only when a cells the unit of life exhibits what we call normal susceptibility. Any change in the normal susceptibility will interfere with the capacity of pre- determined response and this interference will be reflected in a chain response which ultimately leads to a loss of balance as evidence by the development of disease. As normal susceptibility is essential for the maintenance of health, and disease result from abnormal susceptibility, all rational therapeutics will aim at the restoration of normal susceptibility."
- Dr. M.L.Dhawale, principles and practice of Homoeopathy, Page no-244, edition-2000, by institute of clinical research.
Dr. C. F. S. Hahnemann mentioned it in his organon of medicine's sixth edition in aphorism no 9-" in the healthy condition of man, the spiritual vital force (autocracy), the dynamics that animates the material body (organism), rules with unbounded sway, and retains all the parts of the organism in admirable, harmonious, vital operation, as regards both sensation and function, so that our indwelling, reason- gifted mind can freely employ this living, healthy instrument for the higher purposes of our existence."
In other aphorism no 10 He mentioned that " The material organism, without the vital force , is capable of no sensation, no function, no self preservation, it derived all sensation and performs all the functions of life solely by means of the immaterial being ( the vital principle) which animates the material organism in health and in disease."
On the other hand , according to the concept of Dr H A Robert he mentioned it in his book the principle and art of cure by Homoeopathy in Page no 35 under chapter of vital force as -" we recognize life in three parts, the body, the mind and the spirit. This is a trinity and this trinity is always present in all life and in some form in every parts of our organism. These force react in sympathy and are inter dependent. We are prone to think of attained life as composed of those three member's which make it a trinity, but we must remember also that is a unity from its inception. When the two parent cell are united that vital principal, the vital energy, is Already present ; and the ego of the completed cell dose not change one after once beginning its process; it has in itself and of itself the power to develop the cell, the physical Al, because of the continual flowing through them of the vital energy that dominates the whole."
On the other concept of Dr Stuart close he mentioned it in his book of The Genius of Homoeopathy in page no 60- " Life is the invisible, substantial, intelligent, individual, coordinating power and cause directing and controlling the forces involved in the production and activity of any organism possessing individuality. Health is that balanced condition of the living organism in which the integral, harmonious performance of the vital functions tends to the preservation of the organism and the normal development of the individual."
So normal susceptibility is the normal function of vital principle.