At a recent meeting of the Physiological Society, Dr. J. Munk reported on
experiments instituted by him in the course of the last two years with a
view of arriving at an experimental decision between the two theories of
the secretion of urine--the filtration theory of Ludwig and the secretion
theory of Heidenhain. According to the first theory, the blood pressure
prescribed the measure for the urine secretion; according to the second
theory, the urine got secreted from the secretory epithelial cells of the
kidneys, and the quantity of the matter secreted was dependent on the rate
of movement of the circulation of the blood. The speaker had instituted his
experiments on excided but living kidneys, through which he conducted
defibrinized blood of the same animals, under pressures which he was able
to vary at pleasure between 80 mm. and 190 mm. Fifty experiments on dogs
whose blood and kidneys were, during the experiment, kept at 40° C.,
yielded the result that the blood of starving animals induced no secretion
of urine, which on the other hand showed itself in copious quantities where
normal blood was conducted through the kidney. If to the famished blood was
added one of the substances contained as ultimate products of digestion in
the blood, such, for example, as urea, then did the secretion ensue.
The fluid dropping from the ureter contained more urea than did the blood.
That fluid was therefore no filtrate, but a secretion. An enhancement of
the pressure of the blood flowing through the kidney had no influence on
the quantity of the secretion passing away. An increased rate of movement
on the part of the blood, on the other hand, increased in equal degree the
quantity of urine. On a solution of common salt or of mere serum sanguinis
being poured through the kidney, no secretion followed. All these facts,
involving the exclusion of the possibility of a central influence being
exercised from, the heart or from the nervous system on the kidneys, were
deemed by the speaker arguments proving that the urine was secreted by the
renal epithelial cells. A series of diuretics was next tried, in order to
establish whether they operated in the way of stimulus centrally on the
heart or peripherally on the renal cells. Digitalis was a central diuretic.
Common salt, on the other hand, was a peripheral diuretic. Added in the
portion of 2 per cent. to the blood, it increased the quantity of urine
eight to fifteen fold. Even in much less doses, it was a powerful diuretic.
In a similar manner, if yet not so intensely, operated saltpeter and
coffeine, as also urea and pilocarpine. On the introduction, however, of
the last substance into the blood, the rate of circulation was accelerated
in an equal measure as was the quantity of urine increased, so that in this
case the increase in the quantity of urine was, perhaps, exclusively
conditioned by the greater speed in the movement of the blood. On the other
hand, the quantity of secreted urine was reduced when morphine or strychine
was administered to the blood. In the case of the application of
strychnine, the rate in the current of the blood was retarded in a
proportion equal to the reduction in the secretion of the urine.
The speaker had, finally, demonstrated the synthesis of hippuric acid and
sulphate of phenol in the excided kidney as a function of its cells, by
adding to the blood pouring through the kidney, in the first place, benzoic
acid and glycol; in the second place, phenol and sulphate of soda. In order
that these syntheses might make their appearance in the excided kidney, the
presence of the blood corpuscles was not necessary, though, indeed, the
presence of oxygen in the blood was indispensable.
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