874 PHYSIOLOGY OF DIGESTION AND SECRETION. 



proof that the thymus is connected with growth falls in very well 

 with what is stated above in regard to the importance of this 

 organ during the prepubertal period. 



Adrenal Bodies. The adrenal bodies or, as they are frequently 

 called in human anatomy, the suprarenal capsules belong to the 

 group of ductless glands. It was shown first by Brown-Se*quard 

 (1856) that removal of these bodies is followed rapidly by death. 

 This result has been confirmed by many experimenters, and so far 

 as the observations go the effect of complete removal is the same 

 in all animals. The fatal effect is more rapid than in the case of 

 removal of the thyroids, death following the operation usually in 

 two to three days, or, according to some accounts, within a few 

 hours. The symptoms preceding death are great prostration, mus- 

 cular weakness, and marked diminution in vascular tone. These 

 symptoms resemble those occurring in Addison's disease in man, 

 a disease which clinical evidence has shown to be associated with 

 pathological lesions in the suprarenal capsules. These older ob- 

 servations indicated clearly enough that the adrenal glands are of 

 essential importance to the life of the organism, but the first indi- 

 cation as to the nature of its activity was furnished by the dis- 

 covery, made by Oliver and Schafer,* of the remarkable effects 

 observed when an extract of the medulla of the gland is injected 

 into the circulation of a living animal. Briefly stated, the effect 

 of such an injection is a pronounced slowing of the heart-beat 

 together with a rise of pressure. The slowing of the heart-beat is 

 due to a stimulation of the cardio-inhibitory center, for if the 

 vagi are cut before making the injection this result drops out; 

 the blood-pressure, on the contrary, not being restrained by the 

 slowing of the heart, rises rapidly and may reach an extraordinary 

 height. The explanation of the effect of the extracts on blood- 

 pressure is given below. 



Since effects of this kind were not obtained from extracts of the 

 cortex of the gland, it was apparent from these initial experiments 

 that possibly in the adrenal, as in the thyroid tissue, there are 

 two organs or tissues to be considered whose functions may 

 be very different. Subsequent investigations have served to 

 strengthen this belief. The cortical and medullary tissues are 

 separate anatomically from each other in some of the fishes, and it 

 has been proposed to speak of the cortical tissue as the interrenal 

 system and of the medulla as the adrenal or the chromaffin sys- 

 tem, but for our purpose it will be simpler to state briefly the 

 main facts that have been obtained under the headings cortex 

 and medulla. 



* Oliver and Schafer, "Journal of Physiology," 18, 230, 1895. 



