SECRETION. 325 



transformation of their organic constituents ; and this new substance 

 is discharged also into the excretory duct and mingled with the 

 other ingredients of the secreted fluid. A true secretion, therefore, 

 is produced only in its own particular gland, and cannot be formed 

 elsewhere, since the glandular cells of that organ are the only 

 ones capable of producing its most characteristic ingredient. Thus 

 pepsine is formed only in the tubules of the gastric mucous mem- 

 brane, pancreatine only in the pancreas, tauro-cholate of soda only 

 in the liver. 



One secreting gland, consequently, can never perform vicariously 

 the office of another. Those instances which have been from time 

 to time reported of such an unnatural action are not, properly 

 speaking, instances of "vicarious secretion;" but only cases in 

 which certain substances, already existing in the blood, have made 

 their appearance in secretions to which they do not naturally belong. 

 Thus cholesterine, which is produced in the brain and is taken up 

 from it by the blood, usually passes out with the bile; but it may 

 also appear in the fluid of hydrocele, or in inflammatory exuda- 

 tions. The sugar, again, which is produced in the liver and taken 

 up by the blood, when it accumulates in large quantity in the cir- 

 culating fluid, may pass out with the urine. The coloring matter 

 of the bile, in cases of biliary obstruction, may be reabsorbed, and 

 so make its appearance in the serous fluids, or even in the perspira- 

 tion. In these instances, however, the unnatural ingredient is not 

 actually produced by the kidneys, or the perspiratory glands, but 

 is merely supplied to them, already formed, by the blood. Cases 

 of "vicarious menstruation" are simply capillary hemorrhages 

 which take place from various mucous membranes, owing to the 

 general disturbance of the circulation in amenorrhoea. A true 

 secretion, however, is always confined to the gland in which it 

 naturally originates. 



The force by which the different secreted fluids are prepared in 

 the glandular organs, and discharged into their ducts, is a peculiar 

 one, and resident only in the glands themselves. It is not simply 

 a process of filtration, in which the ingredients of the secretion 

 exude from the bloodvessels by exosmosis under the influence of 

 pressure ; since the most characteristic of these ingredients, as we 

 have already mentioned, do not pre-exist in the blood, but are 

 formed in the substance of the gland itself. Substances, even, 

 which already exist in the blood in a soluble form, may not have 

 the power of passing out through the glandular tissue. Bernard 



