The Precocious Discovery of Erythrocyte Deformability: Giuseppe Saverio Poli's 18th-Century Insight

The Precocious Discovery of Erythrocyte Deformability: Giuseppe Saverio Poli’s 18th-Century Insight Amelia Carolina Sparavigna1 and Gemini (Modello Linguistico di Google)2 1 DISAT, Politecnico di Torino, 2 Gemini AI DOI: 10.5281/zenodo.17634031 Abstract: This article re-examines the historical work Elementi di Fisica Sperimentale (Elements of Experimental Physics, Venice, 1796) by Giuseppe Saverio Poli (1746–1825) to contextualize and emphasize his pioneering contribution to 18th-century microscopy and physiology. The analysis focuses, in particular, on Poli’s observations regarding red blood cells (erythrocytes). While the scientific polemic of the era (involving figures like Della Torre, Fontana, and Caldani) centered on the controversial static shape of the erythrocyte, Poli offered a unique dynamic description: he observed how red blood cells were forced to disintegrate into particles, align, and immediately reform to traverse extremely narrow passages ("stretto angustissimo"). This description, obtained with the primitive microscopes of the time, surprisingly anticipates the principle of erythrocyte deformability (or cell squeezing)—a fundamental mechanism for microcirculation and the passage of blood cells through capillaries, the validity of which was definitively confirmed only by sophisticated 21stcentury microfluidic experiments. This paper establishes Poli not merely as a meticulous educator of Experimental Physics, but as a precursor whose acute observations laid the groundwork for modern applied biophysics. This analysis is based on the article "Microscopi, Eritrociti e Protisti nelle Lezioni di Fisica Sperimentale di Giuseppe Saverio Poli" by Amelia Carolina Sparavigna, Philica, 2018, available https://hal.science/hal-01694310/ . 1. Context: Experimental Physics and the Enlightenment Giuseppe Saverio Poli (1746–1825) was a prominent physician and naturalist in Naples during the late 18th century. His extensive work, Elementi di Fisica Sperimentale (Elements of Experimental Physics), first published in Venice in 1796, stands as one of the first Italian-language textbooks on the subject. Poli’s work reflects the influence of the Enlightenment, where the classical, philosophical view of physics was giving way to a science grounded in controlled experiments and observations. Notably, Poli's Experimental Physics was highly focused on practical applications, making it a form of Applied Physics that embraced diverse fields, including medicine and biology. 2. Microscopy, Father Della Torre, and the Red Blood Cell Polemic Poli's discussion of the simple microscope in his lesson XXIV (Article 1, Paragraph 1561 of the 1817 edition) serves as the backdrop for his physiological observations. He details the function of the simple microscope, explaining that magnification increases as the focal distance decreases. This principle led to the adoption of small glass spheres as lenses, an innovation perfected by Father Giovanni Maria della Torre (1710–1782). Using these highly effective sphere microscopes, Della Torre made the then-controversial claim that human red blood cells appeared as "ciambellette" (small rings or doughnuts) or collections of small sacs joined in a circle, thus being hollow in the middle. This claim triggered a vivid European polemic:  Della Torre’s views were immediately contradicted by other distinguished observers like Felice Fontana, who asserted a purely spheroidal shape.  The English physiologist William Hewson later suggested a plano-rotund (flattened disc) shape, but still claimed an internal nucleus.  Later, anatomist Leopoldo Caldani verified Della Torre’s observation of the ring-shape, but definitively argued that the perceived central hole was merely an optical illusion—an effect common to small, non-spherical, translucent fragments under the microscope. 3. Poli’s Original Contribution: The Dynamic Observation Amidst this debate, Poli himself conducted observations alongside Della Torre and offered a unique, dynamic verification of the cell’s pliability—an observation far more significant than the debate over the static shape. Poli recounts his experience in the 5th volume of his Elements:  He described seeing the red blood cell "doughnuts" floating in the serum until they reached a "stretto angustissimo" (a very narrow strait) formed by blood clots.  Unable to proceed because their diameter was larger than the strait’s width, the cells dissolved into their constituent particles.  The particles then lined up ("ordinarono in fila") to secure passage through the gap.  Crucially, as soon as they reached open water, the component particles immediately curved back together ("curvaronsi immediatamente in giro") to form the ring shape anew. Poli's account is a remarkable, pre-modern description of Erythrocyte Deformability. This is precisely the mechanism by which red blood cells navigate the body:  The diameter of the capillaries is only slightly smaller than that of a single erythrocyte.  The cells must pass one by one and are necessarily deformed in the process. 4. A Link to Modern Biophysics Poli's observation, made nearly three centuries ago, serves as a pioneering link between 18th-century experimental physics and modern biophysics. The validity of his observation was confirmed in the 21st century by technology he could not have imagined. For instance, the Massachusetts Institute of Technology (MIT) published an experiment in 2007 demonstrating precisely how an erythrocyte changes its shape to pass through a microfluidic channel (4 microns in diameter). See please: Trafton, A. (2007). MIT shows how blood cells change shape. March 12, 2007 MIT News. This historical account highlights Poli not just as a meticulous educator, but as a pioneering observer whose early work anticipated one of the fundamental principles of blood flow and microcirculation. Conclusions The re-examination of Giuseppe Saverio Poli's Elementi di Fisica Sperimentale, conducted in this work, elevates its status beyond a simple didactic manual, revealing it as a source of surprisingly farsighted scientific insights. Poli's description of the dynamic behavior of erythrocytes is significant for three fundamental reasons: 1. Physiological Priority: His observation stands as one of the earliest and most accurate testimonies of cellular deformability in the context of microcirculation. Poli shifted the focus from the inconclusive debate over the static shape (the "doughnut") to the fundamental mechanical and dynamic function of the cell. 2. Disciplinary Synthesis: Poli, as a professor of Experimental Physics, demonstrates how his discipline was intrinsically an Applied Physics, capable of penetrating and informing the principles of biology and physiology, thus establishing a conceptual bridge that today we would recognize as biophysics. 3. Historical Validation: The fact that an intuition obtained with the limited instrumentation of the 18th century (Della Torre’s microscope) finds perfect correspondence with modern experiments (such as those utilizing microfluidic channels) underscores the timeless quality and accuracy of his observational method. In summary, the analysis of Poli’s text credits him not only as a disseminator of Enlightenment scientific concepts but as a pioneer whose applied methodology and direct observations anticipated one of the core principles of hemodynamics and cellular physiology by centuries.