30 LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE 



of the suprarenal capsules. A short time after this observation a French 

 physiologist, Brown- Sequard, found that animals from which the supra- 

 renal capsules are removed rarely survive the operation for more than a 

 few days. In the concluding decade of the last century interest in these 

 bodies was revived by the discovery 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 sympathetic nervous system (Lang- 

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

 although we have still much to learn regarding their functions. 



Another instance of an internally secreting gland which is essential 

 to life, or at least to its maintenance in a normal condition, is the thyroid. 



The association of imperfect development or disease 

 of the thyroid with disorders of nutrition and inactivity 

 of the nervous system is well ascertained. The form of idiocy known as 

 cretinism and the affection 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 or cured by the administration of its juice. On the other 

 hand, enlargement of the thyroid, accompanied by increase of its secre- 

 tion, produces symptoms of nervous excitation, and similar symptoms 

 are caused by excessive administration of the glandular substance by 

 the mouth. From these observations it is inferred that the juice contains 

 hormones which help to regulate the nutrition of the body and serve 

 to stimulate the nervous system, for the higher functions of which they 

 appear to be essential. To quote M. Gley, to whose researches we 

 owe much of our knowledge regarding the functions of this organ : * La 

 genese et 1'exercice des plus hautes faculte's de 1'homme sont conditionne"s 

 par 1' action purement chimique d'un produit de se'cre'tion. Que les 

 psychologues me"ditent ces faits ! ' 



The case of the parathyroid glandules is still more remarkable. 

 These organs were discovered by Sandstrom in 1880. They are four 



minute bodies, each no larger than a pin's head, 

 imbedded in the thyroid. Small as they are, their 

 internal secretion possesses hormones which exert a powerful influence 

 upon the nervous system. If they are completely removed, a complex 

 of symptoms, technically known as ' tetany,' is liable to occur, which 

 is always serious and may be fatal. Like the hormones of the thyroid 

 itself, therefore, those of the parathyroids produce effects upon the 

 nervous system, to which they are carried by the blood ; although the 

 effects are of a different kind. 



Another internally secreting gland which has evoked considerable 

 interest during the last few years is the pituitary body. This is a small 

 structure no larger than a cob-nut attached to the base of the brain. 

 It is mainly composed of glandular cells. Its removal has been found (by 



