This section is from the book "The Home Hand-Book of Domestic Hygiene and Rational Medicine. Volume 2.", by J. H. Kellogg, M.D.. Also available from Amazon: The Home Hand-Book of Domestic Hygiene and Rational Medicine, Volume 2.
This condition has already been described as being one in which there is an excitement or increased intensity of vital action.
The causes of irritation, in the sense in which we are here considering it, are chiefly an increased intensity of the so-called vital stimuli, or those agents upon which the maintenance of life and health depends, as an excess of food, light, electricity, or mental influence. By any of these agents the vital action of the whole or a part of the organism may be increased to an abnormal extent. Where the excitement is not sufficiently intense to occasion disturbances of other parts of the organism it is called irritation.