This section is from the book "Health Without Medicine. A Treatise On The Laws Of The Human System", by Larkin B. Coles. Also available from Amazon: Philosophy Of Health.
This state of mind has much to do with the healthy action of the physical system. A cheerful and happy mind gives a free and easy circulation in the nervous system; it aids in the generation of animal electricity or nervous fluid, which gives support to the vital energies of the whole body. Cheerfulness, by its effect on the nervous system, contributes much toward a healthy and free circulation of the blood. It has to do, indeed, with the formation of the blood, by virtue of its influence on the process of digestion. A cheerful mind, especially during the hour set apart particularly for the first effort of the stomach after a meal, is very important to an easy, thorough digestive process. If the mind be attacked with grief, the food is not digested as well; and consequently the system is not as well nourished. How commonly does leanness of body follow continued grief! Why this? Because grief hinders the process of nutrition. It does it in two ways; it hinders the thorough digestion of the food, so that nutrition cannot as well be extracted from it, and it retards the action of the absorbent vessels themselves, which take up the nutritive part of the food, and convey it into the blood.
Whatever, then, may be an individual's condition or circumstances in life, it will be great economy for him to make himself cheerful and happy. However bitter may be the cause of his grief, let him cultivate a spirit of resignation; however painful may be his condition in life, let him endeavor to be content with such things as he has; however dark his prospects, let him hope for good. While nothing is gained by despondency, much is lost. While cheerfulness helps others to be healthy and happy, it is of great benefit to oneself.
Some have thought that much cheerfulness was contrary to true dignity and Christianity. But this is taking a narrow-minded view of things. It is no more a sin nor a breach of dignity to indulge in real cheerfulness, than it is to take wholesome food. There is a distinction to he made between cheerfulness and levity. While levity may be undignified and unchristian, genuine cheerfulness may be a. part of dignity and Christianity both. Ministers have been sometimes charged with a want of spirituality, because, at some of their social meetings, they indulge in some degree of merriment; but all this is in keeping with nature's law, and is absolutely essential to health. Their situation and calling ordinarily circumscribe them in relation to sources of amusement, and their responsibilities are adapted to induce solemnity of mind; and if this condition could not now and then be relieved, they could scarcely endure it. If we would be benefited by their ministrations, we must give them a chance to live.