THE MECHANISM OF THE SECRETION OF URINE. 
By Ernest H. Staeling. 
Contents. — Theories of Urinary Secretion, p. 639 — Theory of Bowman, p. 639 — 
Theory of Ludwig, p. 640 — Secretion of "Water, p. 641 — Methods, p. 642 — 
The Concentration of the Urine, p. 650 — Heidenhain's Criticism of the Theory 
of Lndwig, p. 652 — Experiments of Xussbaum, p. 655 — Experiments of Bibbert, 
p. 656 — Experiments of Bradford, p. 656 — The Influence of the Nervous 
System on the Secretion of Urine, p. 659. 
Theories of Urinary Secretion. 
In all the organs of the body whose functions have been investigated by 
physiologists, it has heen found that a difference of function is invariably 
associated with a difference in structure, so that the interdependence 
of function and structure has become an axiom. "We are therefore 
justified in founding theories concerning the physiological function of 
an organ on a purely anatomical study of its structure, although the 
complete establishment of such theories must ultimately be afforded 
1 ly physiological invest igati ons. 
The kidney differs from all other secretory glands, in the fact that 
at the blind end of its tubulus we find a structure — the glomerulus — 
where the vascular capillaries abut directly on the lumen of the tubulus, 
without the interposition of any lymph space. Ever since tin' publication 
of Bowman's paper on the Malpighian bodies of the kidney, these have 
been looked upon as the essential source of the water}- constituents of 
the urine. 
Theory of Bowman. — Bowman, 1 who founded his theory of urinary 
formation exclusively on the anatomical structure of the kidney in 
various animals, concluded that "as the tubes and their plexus of 
capillaries were probably the parts concerned in the secretion of that 
portion of the xu'ine to which its characteristic properties are due (the 
urea, lithic acid, etc.), the Malpighian bodies might be an apparatus 
destined to separate from the blood the watery portion." 
The folio whig are the grounds on which Bowman based this 
hypothesis : — 
(a) That the tubes are secretory. 
(1) The extent of surface obtained by the involutions of the 
tubules. 
(2) The fact that the hiring membrane of the tubules is formed 
by thick epithelial cells, similar to those fotmd on the 
secreting surface of all true glands. 
1 Phil. Trans., London, 1S42, p. 57. 
