232 THE INTERNAL SECRETIONS—1920 
16. Constant chilliness. 16. Unbearable sensation 
17. Difficult and slow of heat. 
respiration. 17. Superficial respira- 
18. Increase in weight. tion, slight expansion 
19. Senile appearance, of thorax. : 
even in young people. 18. Loss of weight. 
19. Youthful, luxuriant 
development, at least 
in the earlier stages. 
One can see from this table how diametrically op- 
posed to each other are the symptoms produced. Ir 
fact, we have before us two different types of individ- 
uals, whose physical and mental contrasts cannot, in- 
deed, be more outspoken. While the symptoms enumer- 
ated in the left-hand table are produced by extirpation 
of the thyroid gland, we find more or less similar symp- 
toms in cretins and myxedematous patients, whose 
thyroid gland is either atrophied or destroyed. On the 
other hand, when we consider the fact that artificial 
Graves’s disease was induced experimentally by feed- 
ing individuals with the desiccated product of the 
gland, there can be hardly any doubt that this chain of 
different symptoms is produced in the first instance by 
the lack of the thyroid hormone; and in the second, by 
its overabundance. 
It is clear that this thyroid hormone now isolated in 
chemical form by Kendall, exerts a powerful influence 
over the metabolism and nutrition of the organism, 
hence upon its growth and normal development. The 
normal senility and old age, like the premature senility 
of myxedema, might be the result of the same etiolog- 
ical factor, namely, the lessened activity of the thyroid 
gland. 
In this connection we will cite again from Biedl (2) 
a very interesting passage: ‘The foundation for the 
theory that old age results from changes in the thyroid 
gland lies in the fact, commented upon by Horsley, that 
