566 A MANUAL OF PHYSIOLOGY 



the left and right rotatory moieties have been separated. The 

 former has exactly the same power of raising the blood-pressure 

 as the natural adrenalin, the latter only r L to r V as much. 

 Practically the same proportion holds when the power of the 

 two isomers in producing glycosuria is compared. This con- 

 stitutes important corroboration of the view already referred 

 to (p. 522) that adrenalin glycosuria is caused by an action on 

 the sympathetic system. For the effect on the blood- pressure 

 is known to be thus produced (Cushny). The function of the 

 cortex is unknown. It is stated that it contains cholin, a sub- 

 stance which lowers the blood-pressure, instead of raising it, as 

 adrenalin does. It has been suggested that the adrenal glands 

 have thus a double chemical grip upon the circulation, and can 

 influence it in either direction, just as the bulb can influence it 

 through its double nervous grip. But it is possible that the 

 depressor substance of the cortex may be only a toxic body 

 neutralized or destroyed in the glands. In any case the func- 

 tional difference between cortex and medulla is easily under- 

 stood when we reflect that the morphological history of the two 

 tissues is quite different. The medulla is developed from cells 

 which push their way into the gland from the rudiments of the 

 sympathetic ganglia at that level, and is therefore of ectodermic 

 origin. The cortex is derived from the same mesodermic 

 structure which gives rise to the kidneys and genital organs. 



The existence of secretory fibres for the adrenal glands 

 in the splanchnic nerves has been rendered probable by the 

 experiments of Dreyer, who finds that the amount of active 

 substance in the blood of the suprarenal vein, as tested by its 

 physiological effect when injected into an animal, is increased 

 by stimulation of those nerves. 



Pituitary Body. In the pituitary body three parts may be 

 distinguished : (i) The anterior lobe proper, or pars anterior, 

 consisting of epithelial cells, many of which are filled with 

 granules of the type seen in glandular epithelium, and abun- 

 dantly provided with bloodvessels ; (2) the pars intermedia, 

 consisting of epithelial cells, less granular and less richly supplied 

 with bloodvessels than those of the pars anterior ; (3) the pos- 

 terior lobe proper, or pars nervosa, consisting chiefly of neuroglia 

 closely invested by epithelial cells of the pars intermedia, and 

 invaded by the colloid secreted by these cells. These differences 

 in the structure of the anterior and posterior lobes of the pituitary 

 body correspond to a difference in their development, the anterior 

 lobe, with the pars intermedia, being derived from an inpushing 

 of the ectoderm of the buccal cavity, and the posterior lobe from 

 an extension of the neural ectoderm, which grows backwards as 

 the infundibular process till it meets and blends with that por- 

 tion of the buccal invagination which* gives rise to the pars 



