518 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



or anxiety, will stop the secretion, causing the ''tongue to cleave unto 

 the roof of the mouth," rendering speech difficult or impossible. 

 Such arrest of the salivary secretion also makes the swallowing of dry 

 food difficult. Advantage of this fact is taken in the ''ordeal by 

 rice" which used to be employed in th,e East for the detection of 

 criminals. 



REGULATION BY CHEMICAL AGENTS. 



The activities of the cells constituting our bodies are controlled, as 

 already mentioned, in another way than through the nervous system, 

 viz, by chemical agents (hormones) circulating in the blood. Many 

 of these are produced by special glandular organs, known as injternally 

 secreting glands. The ordinary secreting glands pour their secretions 

 on the exterior of the body or on a surface communicating with 

 the exterior; the internally secreting glands pass the materials which 

 they produce directly into the blood. In this fluid the hormones are 

 carried to distant organs. Their influence upon an organ may be 

 essential to the proper performance of its functions or may be merely 

 ancillary to it. In the former case removal of the internally secreting 

 gland which produces the hormone, or its destruction by disease, may 

 prove fatal to the organism. This is the case with the suprarenal 

 capsules, small glands which are adjacent to the kidneys, although 

 having no physiological connection with these organs. A Guy's 

 physician, Dr. Addison, in the middle of the last century showed that 

 a certain affection, almost always fatal, since known by his name, is 

 associated with disease of the suprarenal capsules. A short time after 

 this observation a French physiologist, Brown-Sequard, found that 

 animals from which the suprarenal capsules are removed rarely sur- 

 vive the operation for more than a few days. In the concluding dec- 

 ade of the last century interest in these bodies was revived by the dis- 

 covery that they are constantly yielding to the blood a chemical 

 agent (or hormone) which stimulates the contractions of the heart 

 and arteries and assists in the promotion of every action which is 

 brought about through the S3anpathetic nervous system (Langley). 

 In this manner the importance of their integrity has been explained, 

 although we have still much to learn regarding their functions. 



THYROID AND PARATHYROIDS. 



Another instance of an internally secreting gland which is essential 

 to life, or at least to its maintenance in a normal condition, is the thy- 

 roid. The association of imperfect development or disease of the 

 thyroid with disorders of nutrition and inactivity of the nervous sys- 

 tem is well ascertained. The form of idiocy known as cretmism and 

 the afTcction termed" myxoedema" are both associated with deficiency 

 of its secretion; somewhat similar conditions to these are produced 

 by the surgical removal of the gland. The symptoms are alleviated 



