The most iconic book of medicine ever, Gray's Anatomy, is the product of a brilliant and tragic partnership. Henry Gray was a meticulous London anatomist, but the detailed, masterful illustrations were the work of Henry Vandyke Carter, a skilled physician and draftsman. Carter, who later had a distinguished career in India, worked for 18 months on the drawings. Yet, in a lasting slight, the original title page read “Anatomy, Descriptive and Surgical by Henry Gray… with Drawings by H.V. Carter.” His secondary credit and modest, lump-sum payment of £150—for images that would become iconic—remains a historical injustice. An early anecdote highlights the book’s practical aim. To ensure accuracy, Gray and Carter reportedly dissected an unclaimed pauper’s body from the St. George’s Hospital morgue together, with Gray naming structures and Carter sketching in situ. This collaboration between hand and eye, scalpel and pen, created an unprecedented clarity that fused art with science, securing the book’s place as a medical touchstone for over 160 years. Gray was only 34 when he died of smallpox in 1861, just three years after his seminal work’s first publication. He never saw its monumental, enduring success.

Today you are going to discover the most intense love story ever told. A union that revolutionised biotechnology and, at the same time, taught us why we should not eat raw egg. To avoid any misunderstanding, I am referring to molecular love, and to another aspect of the egg quite apart from microbial food safety. Let’s get into it. Egg white is composed of approximately 90% water and 10% protein. And here is the key point: these proteins contain all the essential amino acids the body needs and cannot synthesise on its own. That is why their biological value is 100, meaning they are used almost completely for the body’s own protein synthesis. But egg white is far more than a protein source. It is a viscous, sophisticated, biochemically active matrix, designed to nourish and protect the embryo in an environment that, from the very first moment, is vulnerable to microbial contamination. Its proteins can be classified into two functional groups: - Nutritive, which supply the embryo with amino acids, cofactors and vitamins. - Defensive, which act as a chemical and enzymatic barrier against microorganisms that may enter through the porous shell. Why so many defences in something we think of simply as food? Because from the moment it is laid, the egg is exposed to bacteria from the environment, the shell, and the hen’s reproductive tract. And since it has no immune system of its own, it depends entirely on its protective molecular architecture. The egg is not a sterile environment. Its shell is porous, and although it has a protective cuticle, it remains susceptible to bacterial colonisation. The egg white acts as a chemical barrier against these attacks. Each protein has a specific mission: some destroy bacteria, others deprive them of essential nutrients such as iron, and others block their enzymes or immobilise them within a viscous network. It is a complete defence system, without the need for immune cells. In short: - Ovotransferrin sequesters the iron bacteria need. - Lysozyme destroys their cell walls. - Ovomucoid and cystatin block their digestive enzymes - Ovomucin traps them physically in a viscous network. And importantly, Avidin deprives them of biotin, which is essential for their metabolism. And this is the most stable biochemical love story ever observed. Avidin binds to biotin (vitamin B7) with an almost irreversible strength. Its dissociation constant (Kd) lies between 10⁻¹⁴ and 10⁻¹⁵ M. Once bound, they do not separate under normal physiological conditions. It is the highest-affinity interaction in nature. Compare it with other strong molecular interactions and the difference is remarkable. Biotin is an essential water-soluble vitamin. It is found in liver, oily fish, nuts, legumes, egg yolk… and is also produced in part by your intestinal microbiota. When raw egg whites are eaten in excess, active avidin sequesters biotin in the intestine, preventing its absorption. This can lead to a functional deficiency, with symptoms such as: Fatigue Dermatitis Brittle nails Hair loss Mild neuromuscular disturbances Cooking the egg denatures avidin. Problem solved. Why is the avidin–biotin bond so strong? Biotin fits perfectly into a closed hydrophobic pocket within avidin. There are multiple hydrogen bonds and Van der Waals forces. Binding induces a conformational change that physically closes the site, like a molecular trap. But the story does not end there. The avidin–biotin interaction has revolutionised molecular biotechnology. It is a kind of super-molecular Velcro: specific, stable, and extraordinarily useful. It is used in: ELISA Western blot Immunoprecipitation Fluorescence microscopy Protein purification This defensive system also has clinical consequences. Egg is one of the most common food allergens, especially in children. Most egg allergies arise from the white and are caused by proteins that the immune system recognises as dangerous. In summary: egg white is far more than a source of protein. It is a sophisticated biological system, both defensive and nutritive. A biochemical toolbox with clinical, immunological, and technological implications. And all of this begins… inside a simple white shell.