868 PHYSIOLOGY OF DIGESTION AND SECRETION. 



most writers on the subject, removal of the thyroid alone, leav- 

 ing, at least, the external parathyroids uninjured, is followed by 

 the development of a state of chronic malnutrition which expresses 

 itself finally in a condition of cachexia. Following a terminology 

 sometimes used in medical literature, this cachectic condition 

 may be designated as "cachexia thyreopriva," whereas the con- 

 vulsive condition or tetany, formerly also described as a symp- 

 tom of loss of the thyroid, is due rather to removal of the para- 

 thyroid, and may be characterized as "tetania parathyreopriva." 

 It is usually assumed that the thyroid cells form an internal secre- 

 tion containing a specific hormone which acts as a chemical 

 stimulus to other tissues, causing an augmentation of their metab- 

 olism. This view is based upon the results obtained from feed- 

 ing thyroid tissues to animals or to man, and upon observations 

 on clinical cases in which there existed either a deficient or an 

 excessive activity of the thyroid tissue, conditions designated 

 respectively as hypothyroidism and hyperthyroidism. 



Hypothyroidism. — In infants a deficiency in th^'roid tissue is 

 responsible for the condition known as cretinism. In the cretin 

 the growth is stunted, the bones are incompletely ossified, the skin 

 is dry and hairless, the reproductive organs are undeveloped, 

 and there is a marked lack of intelligence. We have a picture, in 

 other words, of incomplete or arrested development. 



In the adult a deficiency in thyroid tissue or a subnormal 

 grade of functional activity leads to the development of myxedema. 

 The skin becomes thickened and is dry and hairless and there is 

 an increased deposition of fat. The total metabolism is markedly 

 lowered and the individual shows mental apathy and dulness. 

 Both of these chronic conditions, cretinism and myxedema, may 

 be removed by feeding thyroid tissue. In myxedematous patients 

 remarkable changes in physical appearance and mentality are 

 produced by this simple therapeutic procedure. 



Hyperthyroidism. — Overdevelopment or overactivity of the 

 thyroids in man gives rise to the condition known as Graves' 

 disease or exophthalmic goiter. In these cases the skin is lax and 

 moist, the metabolism is greatly increased, there is a characteristic 

 protrusion of the eyeballs (exophthalmos), nervousness, a rapid 

 heart-beat, and increased blood-pressure. The treatment for such 

 cases takes the form of surgical removal of part of the thyroid 

 bodies. 



From a physiological standpoint the influence of the thyroid 

 tissue upon the body-metabolism is especially noteworthy. In 

 individuals with atrophy of the thyroids the basal metabohsm 

 may be diminished by as much as 40 per cent., while in cases of 

 Graves' disease it is greatly increased. Thus Du Bois* reports 

 * Du Bois, "Archives of Internal Medicine," 17, 915, 1916 



