Selected monographs.

Date:: 1888

Catalogue details

Licence: Public Domain Mark

Credit: Selected monographs. Source: Wellcome Collection.

152/440 (page 134)

dependent upon pressure. The reason, however, why Heidenhain maintains this plea is that he considers the water of the urine to be derived as a rule only from the Mal- pighian tufts, and not from the capillaries surrounding the uriniferous tubules, in accordance with the opinion hitherto held with regard to the former structures. However, this assumption also seems to be contrary to all analogy and probability, for no true gland yields a secretion free from water.-^ And that the uriniferous tubules, after removal of the glomerular system, can supply a true fluid urine has been proved by Nussbaum in his expei'iments on frogs. The potential constituents of urine, which are constantly present in the blood, form, as I have already mentioned, the stimulus to the secretory activity. When the force of the circulation has been diminished after experimental division of the spinal cord, a proportionately greater quantity of only one of these potential urinary constituents is required in order to excite to secretion the epithelium whose function the retarded supply has impaired. The case must obviously be different under normal conditions of circulation. In the first place, the epithelium of the uriniferous tubules, when in a state of normal nutrition, will react to slighter stimuli; for the blood which circulates around these tubules is, as Ludwig urged, some years ago, concentrated by the escape of water, and therefore conveys proportionately more urinary materials to the epithelium. There is also this other fact to be con- sidered, viz. that in the present case several urinary con- stituents (urea, uric-acid-salts, chloride of sodium, &c.) co- operate, and may, under normal conditions, produce an effect identical with that which under abnormal conditions (after division of the spinal cord, &c.) is evoked by a larger- quantity of a single constituent. It must, therefore, be con- sidered as proved that a portion of the water of the urine, and doubtless the smaller portion, is supplied by the epithe- lium of the uriniferous tubules, and is a product of true glandular activity. If, therefore, the watery constituent of the urine is not always excreted in such quantity as Lud- wig's theory of filtration would lead us to anticipate, the . ^ In the sebaceous glands there is no real secretion, but only proliferation, and fatty metamorpiiosis of the epithelium.