Meet the 9th-century Muslim polymath who discerned smallpox from measles

Abu Bakr Muhammad Ibn Zakariya Al Razi was the early advocate of applying a rigorous evidence-based scientific approach to medicine. He was the first person to draw a distinction between smallpox and measles and also conclude that the former disease occurs only once in a lifetime. 

Born in Rayy, near present-day Tehran, in 865, Al Razi was a polymath with a sharp focus on general medicine, philosophy, chemistry, music and mathematics. For his outstanding contributions to science, he became known as Rhazes in the West.

He wrote at least 224 books on various subjects but one of his most influential works is ‘Al Hawi fi al Tibb’, a medical encyclopedia known as ‘Liber Continens Europe’, which became a key reference point to the scientific progress of European societies. While writing the book, he surveyed Greek, Syrian and early Arabic medicine as well as some Indian medical knowledge.

Al Razi's tenacious grip on the fields of chemistry, mathematics and medicine led to his discovery of sulphuric acid, the king of acids. His understanding of medicine also drove him to write the first monograph on paediatrics, known in Latin as Practica Puerorum, which described smallpox and measles in detail. He is also known to be the pioneer of applied neuroanatomy and neurology, and successfully treating various mental illnesses. 

Al Razi's deep knowledge of a broad range of subjects earned him a reputation of being among the greatest physicians of his time. He attracted students from various regions and backgrounds.

Al Razi explained the causes and consequences of several chemical reactions, describing  20 elements that could be applied to investigating chemicals. From a biological perspective, he developed a primitive classification system and divided substances into animals, plants and minerals which paved the way for organic and inorganic chemistry.

In neurology, Al Razi stated that nerves had motor or sensory functions and described seven cranial and 31 spinal nerves, assigning them a numerical order right from the optic to the hypoglossal nerves. 

In his groundbreaking books called ‘Kitab al Hawi’ and ‘Al Mansuri Fi At-Tibb’, Al Razi showed an outstanding ability to localise lesions, described therapeutic options and reported clinical observations while emphasising the correlation between the anatomic location of a lesion and the clinical signs. As an expert surgeon, he was the first to use opium as anaesthesia.

The knowledge of cranial and spinal cord nerve anatomy combined by Al Razi with an insightful use of clinical information to localise lesions in the nervous system. Furthermore, he was first to clearly separate and recognise concussion from other similar neurological conditions. 

Each patient of his was given a sum of money in order to help to provide immediate needs as a part of Al Razi’s discharge planning, and it made him first to apply for psychiatric aftercare. 

Unlike his scientific work, his philosophical writings were neglected for centuries until they were appreciated once again in the 20th Century.