Selected monographs.

Date:: 1888

Catalogue details

Licence: Public Domain Mark

Credit: Selected monographs. Source: Wellcome Collection.

151/440 (page 133)

Kal cells wliicli cover tlie tufts. Nevertheless tliere is some justification for tlio reasons whicli have caused Heidenhain to give up so completely the filtration theory. So far as they relate to the excretion of the so-called specific con- stituents of urine, and these latter are regarded as a product of secretion by the epithelium of the uriniferous tubules, and not the result of filtration, there can, as I said before, be no question as to their correctness. It is, in some measure, these same reasons which have induced Heidenhain to allow that the process which takes place in the kidneys in general is one of secretion, and not of filtration, and have, therefore, caused him to place these organs on the same footing with all other glands in which indubitably no mere process of filtration takes place. For, as he veiy justly says, as regards all other glands, without exception, we know defi- nitely that the passage of water out of the blood into the secretion-sijaces does not depend upon simple filtration. ^ But, according to my judgment, this very comparison with all other glands would necessarily prevent us from expecting that the processes in the kidneys would take the same course. For the kidneys differ in their construction very essentially from all other glands; it is not only by leaving out of consideration the whole system of the Malpighian bodies, with their affei'ent and efferent vessels, that any general comparison can be instituted between the kidneys and other glands. But as they most assuredly possess that system, we ai'e the more justified in expecting differences in the processes of excretion rather than a conformity with those of other glands. From this point of view, therefore, we have certainly no grounds for refusing to admit that filtration takes place in the vascular tufts. Heidenhain thinks that his view is further supported by the fact that the quantity of urine by no means invariably coincides, that is to say, rises and falls, with the increase and diminution of pressure, as would necessarily be the case if the excretion depended upon filtration. This objection can easily be refuted by the state- ment that, in point of fact, the kidney is no mere filtration apparatus, but is in some degree a true gland, and that therefore we must not expect that its action will be entirely