DUCTLESS GLANDS AND INTERNAL SECRETIONS 297 



mesoblast. While nothing is known of the function of the 

 cortex, the medulla yields under experimental inquiry some 

 remarkable and characteristic results. 



An extract of the medulla of the gland when injected into 

 the blood increases both the rate of rhythm and tone of the 

 cardiac muscle, and causes a contraction of the bloodvessels, 

 which produces a remarkable increase in blood-pressure. This 

 increase is of a purely temporary nature, which indicates that 

 the active principle is destroyed in the circulation. Within 

 a few minutes the heart-beats return to the normal and the blood- 

 pressure falls. The active principle known as adrenalin can 

 be detected in the veins leaving the gland, so that there can 

 be no doubt that it is poured into the blood, where it regulates 

 the rhythm and tone of the heart-muscle and maintains blood- 

 pressure. In this important function the adrenals are probably 

 assisted by another internal secretion, to be looked at presently 

 — viz., that from the pituitary body. 



The action of adrenalin in causing constriction of the blood- 

 vessels is turned to account in minor surgery in controlling 

 haemorrhage. 



It is believed that the adrenals possess secretory nerve-fibres 

 derived from the splanchnic, and stimulation of these increases 

 the amount poured into the vein of the gland. Adrenalin acts 

 upon all plain muscle and gland-cells which receive sympathetic 

 fibres, and it is distinctly noteworthy that the effects are identical 

 with those produced by stimulation of the sympathetic fibres 

 (Langley) , of which system the medulla of the gland is, as pointed 

 out above, merely an outgrowth. 



It is probable that the function of the medulla of this gland 

 is concerned in the provision of a substance intimately con- 

 nected with muscular metabolism, especially ' tone,' not only 

 of the skeletal muscles, but also of the muscular fibres of the 

 circulatory system. There is also considered to be some con- 

 nection between the cortex of the adrenals and the sexual system. 

 In rabbits the cortex of the gland becomes twice the normal 

 thickness during pregnancy ; and it is believed that in man a 

 connection exists between the adrenals, the growth of the body, 

 development of puberty, and sexual maturity. 



The Pituitary Body. — This gland consists of an anterior and 

 posterior lobe, the former being glandular in nature, the latter 

 nervous in structure. It is believed that the anterior lobe is 

 connected in some way or other with the nutrition of the skeleton. 

 Enlargements of the pituitary are associated with a singular 

 disease in the human subject — acromegaly — characterised - by 

 an overgrowth of the bones of the face and extremities. The 

 posterior lobe resembles the adrenal medulla in its action on the 



