. The endocrine organs; an introduction to the study of internal secretion . om which the secretion has been discharged, the alveoliare irregular, shrunk, and empty, their walls are folded, and the lining cellsstand prominently out from the limiting membrane. 94 The Endocrine Organs If after a first full dose of pituitary extract has been given, a seconddose succeed it at a short interval, no further flow of secretion from theexhausted mamma can be The effect of the autacoid, therefore,is not—at any rate immediately—to cause the cells to form and secretemilk, but only to cause the a
. The endocrine organs; an introduction to the study of internal secretion . om which the secretion has been discharged, the alveoliare irregular, shrunk, and empty, their walls are folded, and the lining cellsstand prominently out from the limiting membrane. 94 The Endocrine Organs If after a first full dose of pituitary extract has been given, a seconddose succeed it at a short interval, no further flow of secretion from theexhausted mamma can be The effect of the autacoid, therefore,is not—at any rate immediately—to cause the cells to form and secretemilk, but only to cause the alveoli to empty themselves of the milk whichhas been previously formed and secreted within them. The simplestmanner in which one can conceive this to occur is by contraction of (plain)muscular tissue around the alveoli. In support of this conception, I have succeeded in detecting in thewalls of the mammary alveolilong, rod-shaped nuclei im-mediately external to theepithelium. These nucleiexactly resemble those of in-\ . H voluntary muscle-cells, and •- v & >,. probably belong to a thinmuscular layer which is situ-ated, like the muscular tissueof the sweat glands, betweenthe basement membrane andthe epithelium of the action of pituitary ex-tract upon milk secretiondiffers therefore from itseffect upon the secretion ofurine in the fact that in thelast-named case there is anactual stimulation of therenal cells to abstract fluidfrom the blood, whilst in themammary gland there occursmerely a contraction of the walls of the alveoli and discharge of fluidpreviously secreted. Apart from the pouring out of the contents of the alveoli—which, whenthe gland is intact, shows itself as a tendency of the alveoli to emptythemselves towards the nipple,—the pituitary galactagogue has littleor no effect on the total production of milk. This at least is the resultwhich was obtained in the goat by Findlay, and in cows by Gavin. Laterobservers (Hammond, Sutherland Simpson) h
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