= H. E. Karrer
{c}
\b[<H. E. Karrer>] reported <electron microscopy> of the <basement membrane> between <alveolar epithelium> and capillary <endothelium> in mouse <lung>. The 1956 primary paper examined three electron micrographs and described variation in the width of this intervening layer. Its author byline supports the initials used here; no fuller identity is required to explain the documented observation.<The Ultrastructure of Mouse Lung: Some Remarks Regarding the Fine Structure of the Alveolar Basement Membrane by H. E. Karrer>[Primary abstract and byline, Journal of Biophysical and Biochemical Cytology 2(4 Suppl), 287–292]{ref}
This research made a geometrical question important for physiology: how does an observed section relate to the actual thickness of a gas-transfer barrier? Karrer's report explicitly noted that some apparent thickening could result from oblique sectioning. Thus an image difference need not establish a tissue difference.<The Ultrastructure of Mouse Lung: Some Remarks Regarding the Fine Structure of the Alveolar Basement Membrane by H. E. Karrer>[Abstract: variable width and possible oblique-section contribution]{ref}
An original slab calculation isolates that ambiguity. Let a layer have true perpendicular thickness $t$, and let a measurement line make angle $\theta$ with its normal. The line crosses distance
$$
\ell=\frac{t}{|\cos\theta|}.
$$
For $t=100$ nm, normal traversal gives 100 nm, while a line at $60^{\circ}$ gives 200 nm. At an illustrative image scale of 10 nm per pixel, the same physical layer can therefore span 10 or 20 pixels along those different measurement directions. These numbers describe a geometrical model, not Karrer's measured tissue dimensions.
The example is a <section-obliquity ambiguity in barrier thickness>. Instrument <measurement calibration> can establish distance per pixel without establishing the orientation of the tissue. Finite section thickness, preparation and the choice of boundary also belong to the interpretation of an <electron micrograph>.
The scientific contribution is the reported fine structure and its qualified interpretation. A thin structural interface supports investigating <diffusion> across the <alveolar-capillary barrier>, but its image alone does not measure gas solubility, <diffusion coefficient> or physiological gas-transfer capacity. Keeping structure and function distinct makes the observation reusable without claiming more than the experiment established.
Back to article page
