In the early 19th century, better quality achromatic microscopes created the new field of histology - the microscopic study of cells and tissues - which led to a number of neurological revelations. Czech anatomist Johann Purkinje was the first to describe a neuron in 1837. He went on to detail particularly large neurons (now called Purkinje cells) with branching, thread-like extensions in the cerebellum. In 1863, German anatomist Otto Deiters described these extensions (later known as deductions), which conduct messages to neurons, and also identified the cell's axons - thin fibres that conduct messages away from neurons. The first anatomical proof that different parts of the brain performed specific functions was presented in the early 1860s by French anatomist Paul Broca. He discovered that aphasia (the inability to understand and formulate language) was linked to lesions in part of the frontal lobe of the brain (later named Broca's area after conducting autopsies on recently deceased patients). During the 1870s, Italian biologist and pioneering neuroanatomist Camillo Golgi produced detailed descriptions of the spinal cord and the brain's olfactory lobe, cerebellum, and hippocampus. In 1873, he invented a new staining technique using silver nitrate, which showed the intricate structure of neural cells on a microscope slide much more clearly. This was the second great technological enabler. Golgi went on to propose that the brain is made up of a single network (or reticulum) of nerve fibres, through which signals pass unimpeded. This reticular theory was challenged at the time by Spanish neuroscientist Santiago Ramon y Cajal, who argued that the nervous system is a collection of many individual, but interconnected, cells. Cajal's view came to be known as the 'neuron doctrine'. Supported by Sherrington, this theory was proved to be correct in the 1950s, when new electron microscopes were able to show the connections between cells. What technology in the 1950s helped to prove the neuron doctrine?